Roll back also after exceptions raised during queries (#2331)

Roll back also after exceptions raised during queries

It turns out a SQLAlchemy session uses transactions even for queries, so if an exception happens during a query execution, it is necessary to roll back to be able to use the session further.
Related to #2319.

I've been able to reproduce the behavior locally and verify that adding rollbacks to queries makes the PendingRollbackError go away, so I'm quite confident this will work, however I can't be 100% sure 🙂

Reviewed-by: František Lachman <[email protected]>

Author: softwarefactory-project-zuul[bot]