Code review comment for lp://qastaging/~cmiller/desktopcouch/cleaner-exceptions

I got the error below, but thanks for fixing the other problems

===============================================================================
[ERROR]: desktopcouch.records.tests.test_field_registry.TestFieldMapping.test_mergeable_list_field_mapping

Traceback (most recent call last):
Failure: twisted.trial.util.DirtyReactorAggregateError: Reactor was unclean.
DelayedCalls: (set twisted.internet.base.DelayedCall.debug = True to debug)
<DelayedCall 47560752 [0.997409820557s] called=0 cancelled=0 LoopingCall<1.0>(exit_on_success, *(), **{})()>
<DelayedCall 47561184 [1.16833519936s] called=0 cancelled=0 reconnector()>
<DelayedCall 47542144 [28.9974460602s] called=0 cancelled=0 exit_on_timeout()>
-------------------------------------------------------------------------------
Ran 35 tests in 2.731s