Fixed cinder check for non-admin user

It could happen that user doesn't have privileges to perform
list_services. Sahara should use admin user for that.

Refactored keystone client creation to give admin user
access to keystone via API v2.

Change-Id: I275fa07a02f4729f2fc20fcd1f0ea65f3c4d50b2
Closes-Bug: #1375806
Closes-Bug: #1376336
(cherry picked from commit 46ab3f5bfe4c19c3fc028158af705ebde595f355)