Include alembic versions directory to the package
Include alembic versions directory to the package

If package is built without access to git metadata, all the migration
scripts are not included in the build. We need to explicitly specify to
package the scripts.

This patch also removes non-existing files from MANIFEST.in

Change-Id: I9a2acad13271863ee94de63c2404e8697ea70601
Related-bug: #1505628

openstack/neutron-vpnaas,openstack/neutron-vpnaas