Add test_port_shut_down API test

This patch adds test which replaces fullstack test:
neutron.tests.fullstack.test_port_shut_down.PortShutDownTest

It is simple API test which can be done quickly in
neutron-tempest-plugin job. In fullstack instead it requires to prepare
whole environment with neutron-server, fake compute node, agents, etc.
so it takes much more time.

Change-Id: Ica5e72ab6d4c20fdcbd1f0dd38e6adcf627bcefd
1 file changed