Add a serial full tox job to tox.ini

This commit adds a new tox job for running a full tempest job but
serially. Since neutron tenant isolation was fixed we don't have a
test run for the not tenant isolated path. This is the first step in
setting up a periodic non-isolated serial job.

Change-Id: I886b3fd416b2063df5daaca8d17ac6fbbdfe399e
Merge "Add a serial full tox job to tox.ini"