[1079225] Graphs of sub-level resources in groups fail
API's dealing with Resource Groups should typically handle all 3 types of
resource groups: standard, autogroup and autoclusters.  The way to do this
is to use an EntityContext in the API.  In this case we were ignoring
autoclusters.  This fix converts a few group-related APIs to use
EntityContext. It simplifies the APIs, fixes this bug and likely fixes
a few other problems.