Store auth response body and headers

Keystone V3 provides the token in the response headers which
was previously discarded by Session after authentication. This
modifies that behavior so that the headers are also preserved.

Change-Id: Iedae5ccf06253b5b6fa95dda5861ec3f04b081ef
Modify files to use new session data format

Change-Id: If0743afb245a4255062258bbcea297ef276b0fa7