Roll back transaction if execution of proc fails

This change to the code the executes stored procedures should abort the transaction if execution of a stored procedure fails.  I need to figure out how to test this, since it will affect all of AG and *not* just the labadmin site...
Are you sure? [see this documentation](https://docs.python.org/2/tutorial/errors.html#defining-clean-up-actions), which suggests it will be executed regardless of what happens (even if the `return` is executed in the `else` portion)