TrivialFix: Remove pending deprecationwarning

Tempest Network Test cases use assertRaiseRegexp [1], which have
been deprecated [2]. This patch fixes the same.

[1]: http://logs.openstack.org/27/290927/1/check/gate-tempest-dsvm-tap-as-a-service/365440a/console.html#_2016-03-10_01_18_35_179
[2]: https://bugs.launchpad.net/python-keystoneclient/+bug/1436957

Change-Id: If105129b57b478932974a06d17be0d46a961c794
Partial-Bug: #1436957
4 files changed