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: I3ac8516a0c15b0816c14074ec5119e317735edd6

.gitreview

@@ -1,4 +1,4 @@
 [gerrit]
 host=review.openstack.org
 port=29418
-project=openstack/ceilometer-tempest-plugin.git
+project=openstack/telemetry-tempest-plugin.git

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 telemetry-tempest-plugin https://git.openstack.org/openstack/telemetry-tempest-plugin
+
+3. run ``stack.sh``
+

devstack/plugin.sh

@@ -0,0 +1,13 @@
+# install_telemetry_tempest_plugin
+function install_telemetry_tempest_plugin {
+    setup_dev_lib "telemetry-tempest-plugin"
+}
+
+if [[ "$1" == "stack" ]]; then
+    case "$2" in
+        install)
+            echo_summary "Installing telemetry-tempest-plugin"
+            install_telemetry_tempest_plugin
+            ;;
+    esac
+fi

devstack/settings

@@ -0,0 +1,3 @@
+GITREPO["telemetry-tempest-plugin"]=${TELEMETRY_TEMPEST_REPO:-${GIT_BASE}/openstack/telemetry-tempest-plugin.git}
+GITDIR["telemetry-tempest-plugin"]=$DEST/telemetry-tempest-plugin
+GITBRANCH["telemetry-tempest-plugin"]=master