Add script to copy neutron api tests from tempest

Add script to copy neutron api tests from tempest

This change adds a script to automate the copying of api tests from
tempest in the style of oslo_incubator.  The target path will be
neutron/tests/tempest and no manual modifications should be made to
this path until such time as neutron api test development is frozen in
tempest and development can proceed in the neutron tree.  Until that
occurs, a policy of manual once-daily synchronization is suggested.

The target path includes the name 'tempest' as a clear indication that
this is not part of neutron, and that once development is allowed to
proceed, its contents should be rewritten and removed until there is
nothing left.

So long as the tests exist in both the tempest and neutron trees,
testing effort will be duplicated.  The larger goal is to have the
tests in question removed from tempest as per the qa guidelines [1],
so this should be temporary.

1: https://wiki.openstack.org/wiki/QA/Tempest-test-removal

Change-Id: I3cd55983e610a1d61aae565f88fe5017edba1090