Tests: Persistence test mixin fix

* The _get_connection method of PersistenceTestMixin
  should take `self` as the first argument.

Change-Id: Ibaaa0d54b408d5e37c6349c63becef919d02fac8
List examples function doesn't accept arguments

Change-Id: Ic8d9e5b8918dd47190d7aa3b6cfbe281307fb1d2
Merge "List examples function doesn't accept arguments"