Fix mig 186 downgrade when using sqlalchemy >= 0.8

This patch fixes an issue that cause tests to break when using
SQLAlchemy 0.8 and newer. The migration was using non-existing column
names in an update query. Referring to a non-existent column in an
insert() or update() construct will raise an error instead of a warning
in SQLAlchemy 0.8.

As an added bonus - this patch adds the downgrade tests for migration
186 (which were missed in the original patch) to ensure there are no
further regressions.

Fixes bug: #1201453

Change-Id: I3c679e95583ee0c1bded5a01ddec6d6212904195
Merge "Fix mig 186 downgrade when using sqlalchemy >= 0.8"