Fix wrong usage of mock methods

There is no assert_not_called() method in mock, as described here:
https://code.google.com/p/mock/issues/detail?id=159
Fix the call to use the mock.called attribute instead.
This patch also uses right method assert_called_once_with instead
of assertCalleOnceWith.

Change-Id: Idc0125db73cd11707ce885813174ec38535dc501
Merge "Fix wrong usage of mock methods"