Adding new test case for zone test suite

1) test_serial_changes_on_update
   Test Scenario:
	# Update Zone's email - Serial has changed
        # Update Zone's TTL - Serial has changed
        # Update Zone's email and description - Serial has changed
        # Update Zone's description - Serial remained the same
   Note: The Description is a metadata field only known to Designate

Change-Id: I7461326d795221c1da4b7ac627d1ffec7c9212df
2 files changed