Fixup docker ci

Add changes required for the docker ci check job to work.

Add sbin to PATH and add users that fail to get added during the setup
stages of devstack-gate, this can be removed once the sbin change gets
into devstack-gate, see I5f6aecb2b1fa9c49f4d15c5d96c005607b05c803

Also add iptables filters to allow the registry container to access
keystone and glance.

Change-Id: I6bf10b0afdf5ae625d4b3e8f673549fe44230bdc
Merge "Fixup docker ci"