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/playbooks/neutron-tempest-plugin-api/run.yaml b/playbooks/neutron-tempest-plugin-api/run.yaml
index 3470bd4..12638cc 100644
--- a/playbooks/neutron-tempest-plugin-api/run.yaml
+++ b/playbooks/neutron-tempest-plugin-api/run.yaml
@@ -27,23 +27,13 @@
         cmd: |
           set -e
           set -x
-          cat << 'EOF' >>"/tmp/dg-local.conf"
-          [[local|localrc]]
-          TEMPEST_PLUGINS='/opt/stack/new/neutron-tempest-plugin'
-          EOF
-        executable: /bin/bash
-        chdir: '{{ ansible_user_dir }}/workspace'
-      environment: '{{ zuul | zuul_legacy_vars }}'
-
-    - shell:
-        cmd: |
-          set -e
-          set -x
           export PYTHONUNBUFFERED=true
           export DEVSTACK_GATE_TEMPEST=1
+          export DEVSTACK_GATE_TEMPEST_ALL_PLUGINS=1
           export DEVSTACK_GATE_NEUTRON=1
           export DEVSTACK_GATE_EXERCISES=0
           export DEVSTACK_GATE_TEMPEST_REGEX="neutron_tempest_plugin.api"
+          export DEVSTACK_LOCAL_CONFIG="enable_plugin neutron-tempest-plugin git://git.openstack.org/openstack/neutron-tempest-plugin"
           export BRANCH_OVERRIDE=default
           if [ "$BRANCH_OVERRIDE" != "default" ] ; then
               export OVERRIDE_ZUUL_BRANCH=$BRANCH_OVERRIDE