Make sure rpc_notifier opts exist

The notifier tests try to override config opts registered by
rpc_notifier, but rpc_notifier may not be imported before those
tests run.  Use import_opt to ensure the options are registered
before the test tries to override them.

Change-Id: I5f01eed286c71ea2706225d2ca0380df153bd975
Closes-Bug: #1275154
Merge "Make sure rpc_notifier opts exist"