Update to latest oslo rootwrap

Update Neutron rootwrap to the latest from oslo-incubator. This allows
to get rid of the DnsMasqFilter (which was already replaced by
EnvFilter) in preparation for the havana release, as well as get a few
bugfixes.

All the changes are coming directly from the Oslo "rootwrap" module
sync.

Change-Id: Ic373710cce0716323f4349414bb5b231f48d9177
Merge "Update to latest oslo rootwrap"