Problem:
When we run nova client unit test, there are lots of UserWarnings
printed on the screen. These warnings mean to remind users not to
use v2.client directly.
Solution:
1. In top level tests such as some tests in test_auth_plugins.py
test_client.py and fixture_data/client.py, we use updated usage
novaclient.client instead of using novaclient.v2.client directly.
2. In v2 unit tests, we clean those warnings with setting direct_use
False.
Change-Id: I70682e54874860f1d67d29325811c9da616bb705
Closes-Bug: #1532711
14f63647e9