Patrole devstack plugin

Adds devstack plugin for Patrole in order to correctly deploy
Patrole.

This commit:
  - Adds the plugin.sh for orchestrating Patrole installation
    via devstack
  - The settings file for declaring global variables; allow
    RBAC_TEST_ROLE to be overriden by global variable
    RBAC_TEST_ROLE (i.e. export RBAC_TEST_ROLE=Member
    from shell will override the rbac role at run time)
  - Removes pre/post_test_hook since that logic is now
    handled by updated infra jobs [0] and by
    the devstack patrole plugin.

[0] https://review.openstack.org/#/c/468939/3/jenkins/jobs/patrole.yaml

Change-Id: I38c02cbcfea9334c9c0c10096e383efa9a9fc474
Implements: blueprint patrole-devstack-plugin
diff --git a/devstack/settings b/devstack/settings
new file mode 100644
index 0000000..670e878
--- /dev/null
+++ b/devstack/settings
@@ -0,0 +1,8 @@
+# Settings needed for the Patrole Tempest plugin
+# ----------------------------------------------
+
+PATROLE_DIR=$DEST/patrole
+TEMPEST_DIR=$DEST/tempest
+TEMPEST_CONFIG_DIR=${TEMPEST_CONFIG_DIR:-$TEMPEST_DIR/etc}
+TEMPEST_CONFIG=$TEMPEST_CONFIG_DIR/tempest.conf
+RBAC_TEST_ROLE=${RBAC_TEST_ROLE:-admin}