add is_keystone_enabled

This is missing, and makes logic much harder for the grenade use
case.

Change-Id: Ib6670096d190e69273256b87e6a67e2b46945a0d
(cherry picked from commit 4f3b66f538937cf0c7f9fdc97e5472f4c77bbe69)
Merge "add is_keystone_enabled" into stable/icehouse