The check-glanceclient-dsvm-functional gate job was failing due to the
functional tests not picking up valid OpenStack credentials.
Update how we aquire credentials -- fixes side effect of how tox 2.0
handles environment variables.
Change-Id: Ia665dc9673d09421508476d05039d2da8a5e1a29
Closes-bug: 1455102
This will allow adding 'check-glanceclient-dsvm-functional' tests in
the gate, similar to:
* check-novaclient-dsvm-functional
* check-keystoneclient-dsvm-functional
* check-neutronclient-dsvm-functional
* etc
Change-Id: Id970db52695db7dc53206aa05fe573995b57aa78