Fix issue with new python-keystoneclient

As new python-keystoneclient 0.6.0 was released, change
https://review.openstack.org/61247 was merged to it. This commit
changed work with keystoneclient adding session to request
processing from the very beginning, that caused empty self.auth
for this session. In fact that led to no auth-token header passed
to Keystone and unauthorised exception from it.

Change-Id: I67baecacde6f9c94152cd34aae03ba59a0a7a580
Closes-Bug: #1281487
Merge "Fix issue with new python-keystoneclient"