Add identity headers while calling glanceclient

Glance and glanceclient have patches up for a no auth
option in glance. In order for that to happen, nova needs to
send in additional information in its headers to glanceclient.
More details:
Some deployments have everything in the same network. And
for long running snapshots this may cause 401s because
token expires. In these cases the reauth is not required
cause nova has already authenticated the user.
This patch does not convert it to no auth. It only makes
it optional for glance users who do want to use that option.
Related patches:
https://review.openstack.org/#/c/37062/
https://review.openstack.org/#/c/36563/

Resolves bug 1200761

Change-Id: Ife02059abbdce7920f1f408b71e9745d777fa770
Merge "Add identity headers while calling glanceclient"