Make hacking test more accurate

Hacking check returns tuple or None, assertTrue/assertFalse doesn't
handle the return results properly. For example, non-tuple return value
also can pass the hacking unit test method.

  * use assertEqual or assertIsInstance instead of assertTrue
  * use assertIsNone instead of assertFalse
  * remove duplicated test data in method test_virt_driver_imports

Change-Id: Iee8b466c3ab2c6437144367cdb874bd2f8839984
Merge "Make hacking test more accurate"