Refactored Neutron tempest plugin directory structure

* switch from neutron.tests.tempest to neutron_tempest_plugin
* Cleaned up README.rst and setup.cfg
* Use neutron_tempest_plugin as a tempest plugin package
* Fixed gitreview
* Keeping flake8 Ignores in tox.ini as tempest plugin is
  imported from neutron codebase.

Change-Id: I42d389836e72813fdeebc797a577f4a8ac2ee603
diff --git a/.gitreview b/.gitreview
index 698048f..64910a0 100644
--- a/.gitreview
+++ b/.gitreview
@@ -1,4 +1,4 @@
 [gerrit]
 host=review.openstack.org
 port=29418
-project=openstack/openstack.git
+project=openstack/neutron-tempest-plugin.git