Make acls for QA program projects consistent

This commit gives a uniform structure to acl groups for the QA program
projects. This mostly entails removing the milestone proposed section
from use for tempest, (since it is no longer needed) and adding ptl
groups for devstack and grenade with permissions to push signed tags.
(although there probably won't be a need to push tags)

The other changes which are required as part of this cleanup, but I
believe require manual intervention are:
 - To add a qa-ptl group which is a member of the tempest-ptl,
   devstack-ptl, and grenade-ptl groups
 - add the ptl groups to their respective core groups
 - Remove openstack-qa-core group (since I'm not even sure what it's
   even used for)
 - Remove tempest-milestone group (after this change lands)

This change and the manual steps can probably wait until after
governance change I42cdbb8dbbc98a3d83b6bb1abcaadefcc0618bb8 lands

Change-Id: I26d9264b54bb6551d0d73fe58c3d19c4a58ad61e
Merge "Make acls for QA program projects consistent"