Pass all identity headers received to glance

There is an upcoming patch in nova which passes identity
headers to glance client. We want to ensure that these get
passed to glance, which in turn with help the no auth
option in glance.

Resolves bug 1200761

Change-Id: Ifbef582aa4e64a2e7a46db43a9cc6cf8c3531dbd
Merge "Pass all identity headers received to glance"