[server] Make cubicweb/server/utils.py flake8-clean

[server] Drop utils's LoopTask and TasksManager classes not used anymore Related to 17057223.

[server] replace repository's tasks manager by a scheduler Repository() does not accept anymore a 'tasks_manager' argument but rather a 'scheduler' argument which is expected to be an instance of sched.scheduler class. The drop the _tasks_manager attribute of the repository and adjust all internal usages of it. In particular, in the 'repo_stats' service we do not export 'looping_tasks' statistics anymore as there's no way to retrieve this anymore from a web instance. Closes #17057223.

[server] introduce a scheduler class to run repository "looping tasks" We just use the sched module from the standard library and introduce a tiny Python2/3 compatibility layer (more for convenience actually). The "looping" aspect of tasks (previously in LoopTask class) is re-implemeted as a `schedule_periodic_task` function. This is a reasonably thin layer as compared to LoopTask/TasksManager classes. Only the "restart" aspect of LoopTask is no longer present as I'm not sure it's worth keeping. The advantage of using this (in addition to eventually dropping our custom code) is that this scheduler class provides a `run` method that blocks the process while running tasks in its queue. So we can rely on this to have a 'scheduler' ctl command (see forthcoming patch) that would only run "looping tasks" without having to implement the "blocking" aspect ourself. Related to #17057223.

web: add options to ignore css compilation and uicache

[skeleton] call includeme from new cube

[etwist] Do not call repository's start_looping_tasks anymore and warn about this We are about to drop this method from Repository class and replace it by a blocking alternative. This is not compatible with how things currently work in a Twisted server implementation. So do not start repository "looping tasks" in Twisted server anymore and issue a warning about this. If someone is interested in restoring the "all-in-one" behavior where the repository runs within a Twisted server, they may start by implementing repository looping tasks using a Twisted mechanism such as, e.g., http://twistedmatrix.com/documents/current/core/howto/time.html and eventually provide the repository with a compatible scheduler instance so that is can register its periodic tasks. At the moment, we lack resources to do this (and maintain the Twisted server of CubicWeb in general). Related to #17057223.

[test] Flake8-clean and use stdlib unittest in cubicweb/server/test/unittest_utils.py

[web] Don't raise ProcessFormError if there is no value specified a03376213747 introduced a slight modification in None / empty string values and with it a regression where an exception is raised on empty values, while we should simply consider no value is specified and return None.

[test] Cleanup imports in unittest_form Remove unused and reorder, + use bare unittest along the way.

Fix log level parameter not taken into account in cwsource log table An error in the jquery selector of the html widget controlling the log level was the cause of this bug. Closes #15772634 (grafted from c9129aae884b476455c8ed1ad802efc3a26503a5)

[pyramid] Drop call to repository's start_looping_tasks method and warn about this We are about to drop the start_looping_tasks method and running "looping tasks" along the WSGI application is not a very good idea. So issue a warning pointing to the forthcoming "scheduler" command. Related to #17057223.

[test] Make unittest_serverctl.py flake8-clean

[wsgi] Drop calls to repo.start_looping_tasks It's unlikely that these implementations were ever used so we do not bother with deprecation or a warning. We just drop the call to this method which should not be called from within a WSGI application. Related to #17057223.

[pyramid] Drop useless "init_instance" module

[server] Drop inexistent "bootstrap" argument in Repository initialization This is a missing bit from 5de78b6fff2e. Unfortunately this code appears to be uncovered by our test suite.

[server] fix a typo in a docstring

[ctl] Load available configurations in "cubicweb-ctl list" Otherwise we rely on associated ctl plugins to be loaded which is arguably orthogonal to configurations.

[web/views] Fix a docstring

[server] Use looping_task method in Repository._prepare_startup()

[skeleton] Drop logging configuration from development.ini This is actually not useful as logging is already initialized and configure "somewhere else" where the repository is started.

[pyramid] Drop retrieval of auth/session secret in all-in-one.conf We actually never supported this in cubicweb, but only in pyramid-cubicweb.

[cwctl] Recommend 'pyramid' before 'wsgi' when twisted is not available Not sure anyone ever really used the latter and the former is certainly more reliable/tested.

[cwctl] Drop message about 'the pyramid cube' in "start" command This is shown when twisted is not importable and we suggest to use 'cubicweb pyramid <appid>' instead. Since 3.24, cubicweb-pyramid got merge in cubicweb so drop this reference in the message.

[cwconfig] Fix two NameError in load_available_configs() This comes from a copy-paste in d92d75b17a85.

[etwist] Drop try/except around definitions of 'all-in-one' configuration and command handlers cubicweb.server is no longer conditionally shipped, neither in python package nor in debian package since 3.24.

[server] Call 'server_startup' hooks at the end of repository "bootstrap" Now that we have guarded all calls to Repository.looping_task() in 'server_startup' hooks we can execute this hooks category at bootstrap step. This way, repositories running without a tasks manager (i.e. those embedded into a WSGI application) will have these hooks triggered.

[pyramid] Drop module-level cache and cleanup looping tasks in tools And use a LRU cache over cached_build_user function. This looping task is problematic because it would not be run from within a WSGI application which does not have a repository with a tasks manager. This pulls an explicit dependency on 'repoze.lru' but it's not a big deal since pyramid already depends on this. RPM spec file not update since it does not even mention pyramid...

[hooks] Return early in server_startup hooks if the repository has not tasks manager

[server] Only register "clean_sessions" looping tasks if repository has a tasks manager This prepares for calling Repository's _prepare_startup() in bootstrap() so that repository instances without a tasks manager running can still have their 'server_startup' hooks triggered (this is particularly useful for BFSS storages).