Allow group includes to be by UUID instead of group ID

Per discussion on-list, the behavior change in 2.5 to only
allow groups by ID is considered a regression for groups
that want to include external groups (like LDAP).

In order to permit smooth migration, we want to allow both
ID and UUIDs to co-exist for the time being.

Change-Id: I0dbdb15b9c62f2dbce64acbc34c515c7b8229c04
24 files changed