Second attempt to fix PostgreSQL deadlock
Second attempt to fix PostgreSQL deadlock

In 14f63fc we tried to fix SQLAlchemy deadlock by reducing the amount of
time spent in the transaction.

Now we try to force the SQL queries order by calling db.session.flush()
once after updating the Taxi object, and once after updating the
VehicleDescription object.

openmaraude/APITaxi,openmaraude/APITaxi