REST session validity not checked in get_volume_info

The fix for bug 1157242 introduced a new bug in Coraid cinder driver
_get_volume_info that the login session is not checked for
validity/timeout.  This change addressesthat issue for all
methods in the CoraidRESTClient class.

Fixes bug 1160459

Change-Id: Ib2d7ebbf3ef8ec35071f51c6168eb9b3af9405e6
Merge "REST session validity not checked in get_volume_info"