Minimize the manual cleanup done for users after test scenarios

[phil-davis]

OCIS PR #1962 improved the cleanup of users when they are deleted. So we should not need to do so much cleanup of user files/shares/... at the end of test scenarios.

• minimise the cleanup of user files [tests-only] Tidy up user cleanup when running on OCIS or reva core#38661 [tests-only] Bump commit id #1984
• minimise cleanup of user shares (in core Provisioning.php afterScenario we might not need to do deleteAllSharesForUser any more, and?)
• look for any other places that we can remove "manual" user cleanup in AfterScenario code

[phil-davis]

We have done all that we can for now. "owncloud" storage still uses some manual cleanup - that a separate issue that can be sorted out if/when the "owncloud storage driver implements a full cleanup of user files on user deletion.