determine_ports() was not adding the nova-placement-api port to the
ports list because it is run under the apache2 service. This fix
enables determine_ports() to get 'nova-placement-api' from the list
of services rather than 'apache2', allowing it to determine the port
that nova-placement-api uses.
Also enable tests/gate-basic-xenial-ocata in this commit.
Change-Id: I8113e911272ee671026bace9f6e0e8c4ce072e6b