Remove use of testtools.helpers.safe_hasattr
Remove use of testtools.helpers.safe_hasattr

The testtools package removed safe_hasattr in version 2.5.0 [1].
Since it is only used in two unit tests, let's replace it with the
built-in hasattr.

[1] - https://github.com/testing-cabal/testtools/blob/2.5.0/NEWS#L31-L34

Change-Id: I57be2d06efe8913805069150bd3f884322a78a42

openstack/python-tackerclient,openstack/python-tackerclient