Fix TestInterfaceWaiters
Fix TestInterfaceWaiters

TestInterfaceWaiters test case were not verifyinf the main waiters
functionality and sometime they could intermittently fail without
reason like seen in below openstack-tox-py27 Zuul check.

https://review.openstack.org/#/c/559069/33

Solve tests methods failure when time.time() returns two consecutive
floats that rounded by int() function is returning two different integers.

This patch also verify the condition verification method are properly
called and that waiters methods actually returns expected part of
returned body.

Change-Id: I0a2081d823b304d58a5a69a8965858bd4f1303a0

cisco-openstack/tempest,masayukig/tempest,masayukig/tempest,openstack/tempest,openstack/tempest,cisco-openstack/tempest