Avoid manipulating DB directly in unit test

Use the parser.Stack class for inserting data into the database in the
watch rule unit tests. If there is direct database manipulation in the unit
tests, it risks falling out of step with the implementation in the code (in
this case, by not supplying the disable_rollback value).

(Required to squash DB migrations, bug 1072949)

Change-Id: I66e5a0093d20222c876f52e626043704777dcb6a
Merge "Avoid manipulating DB directly in unit test"