Adds Grian-UI Devstack plugin

Easy enable deploying Grian-UI on demand by enabling
it as a plugin for Devstack as follows:

enable_plugin grian-ui https://opendev.org/openstack/grian-ui

Having ceilomter and sg-core enabled is required, since
Grian UI relies on those services to retrieve the metrics.

Change-Id: Id90dc6d41be76de105dbb58abad84b974277379c

devstack/plugin.sh

@@ -0,0 +1,39 @@
+# plugin.sh - DevStack plugin.sh dispatch script grian-ui
+
+function install_grian_ui {
+    setup_develop ${GRIAN_UI_DIR}
+}
+
+# check for services enabled
+if is_service_enabled horizon && \
+   is_service_enabled grian-ui; then
+    if [[ "$1" == "stack" && "$2" == "pre-install" ]]; then
+        # Set up system services
+        # no-op
+        :
+    elif [[ "$1" == "stack" && "$2" == "install" ]]; then
+        # Perform installation of service source
+        echo_summary "Installing Grian UI"
+        install_grian_ui
+    elif [[ "$1" == "stack" && "$2" == "post-config" ]]; then
+        # Configure after the other layer 1 and 2 services have been configured
+        echo_summary "Configuring Grian UI"
+        cp -a ${GRIAN_UI_DIR}/src/grian_ui/local/enabled/* ${DEST}/horizon/openstack_dashboard/local/enabled/
+        cp -a ${GRIAN_UI_DIR}/src/grian_ui/local/local_settings.d/* ${DEST}/horizon/openstack_dashboard/local/local_settings.d/
+    elif [[ "$1" == "stack" && "$2" == "extra" ]]; then
+        # no-op
+        :
+    fi
+
+    if [[ "$1" == "unstack" ]]; then
+        # no-op
+        :
+    fi
+
+    if [[ "$1" == "clean" ]]; then
+        # Remove state and transient data
+        # Remember clean.sh first calls unstack.sh
+        # no-op
+        :
+    fi
+fi

devstack/settings

@@ -0,0 +1,5 @@
+# settings file for grian-ui plugin
+enable_service grian-ui
+
+# set up default directories
+GRIAN_UI_DIR=${GRIAN_UI_DIR:=$DEST/grian-ui}