Sync config module from oslo

Add 'config' to openstack-common so that it syncs from Oslo,
move tools/conf -> tools/config to be able to sync from Oslo,
and then sync the changes which are proposed in oslo-incubator
commit Iee6cc05cad70963f2a151f595ac376c9338f5774.

Change-Id: I32a80b0e2aa0e26b9fc78b7546c07e102639374e
Merge "Sync config module from oslo"