Plug leaky impersonation context - EUCA-8742

The impersonation context is updated to cover the administrator check
and subject / credential methods.

EUCA-8742
Binding fix for modify image attribute - EUCA-8747

EUCA-8747
Binding fixes for describe image/instance attribute - EUCA-8748

EUCA-8748
Fix error message for volume size limit - EUCA-8573

EUCA-8573
Merge remote-tracking branch 'origin/dev/sjones/EUCA-8742' into testing
Merge remote-tracking branch 'origin/dev/sjones/EUCA-8573' into testing