Remove recipe[openstack-identity::db] from the identity roles

The db recipe was removed in commit 54e05e5f2e6f57934310c10d418ab263a9eb14bf
on stackforge/cookbook-openstack-identity.  Updating the role to reflect
this.
Add a role for os-infra-caching

openstack-common searches for role infra-caching.  Adding the role
os-infra-cachine (to be consistent with the current naming schema).
I will update openstack-common in a moment.
Merge remote-tracking branch 'origin/role_update2'