[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.
etc/init.d
etc/cubicweb.d
etc/bash_completion.d
usr/bin
usr/share/doc/cubicweb-ctl
var/log/cubicweb
var/lib/cubicweb/backup
var/lib/cubicweb/instances