Add devstack plugin to ease integration tests

Instead of requiring users to install the plugin manually, add a
devstack plugin that can be enabled in order to perform the
installation.

Change the integration tests to use the globally installed plugin
instead of using TEMPEST_PLUGINS.

Change-Id: I7282fa60db15427c73dfef84a40093904e083db2
diff --git a/devstack/README.rst b/devstack/README.rst
new file mode 100644
index 0000000..e605fcf
--- /dev/null
+++ b/devstack/README.rst
@@ -0,0 +1,21 @@
+====================
+Enabling in Devstack
+====================
+
+**WARNING**: the stack.sh script must be run in a disposable VM that is not
+being created automatically, see the README.md file in the "devstack"
+repository.  See contrib/vagrant to create a vagrant VM.
+
+1. Download DevStack::
+
+    git clone https://git.openstack.org/openstack-dev/devstack.git
+    cd devstack
+
+2. Add this repo as an external repository::
+
+     > cat local.conf
+     [[local|localrc]]
+     enable_plugin neutron-tempest-plugin https://git.openstack.org/openstack/neutron-tempest-plugin
+
+3. run ``stack.sh``
+