[dataimport] Add explanation about why external entities can't be inserted By default after the import processed the importer indicates which external entities can't be inserted because they are missing dependency data (other entities, used in inlined or mandatory relations). It usually helps there to find out which extids / relations are missing, so add this to the log.

[querier] Fix typo in Unauthorized message exception

[massive store] Ensure temporary metadata table get dropped even if there is some integrity errors while inserting entity values or setting back index/constraints, or any other errors. In case of exception, rollback to ensure we're not committing undesired intermediate state.

[test] Stop using lgc.testlib.unittest_main in dataimport's test_sqlgenstore.py

[test/cleanup] Cleanup flake8 errors in dataimport's test_sqlgenstore

[pkg] Fix path error in flake8-ok-files 'sources' is a subpackage of 'server'.

[cleanup] Fix undetected pep8 error