Expose enabled plugins for Sahara

Make devstack users able to specify enabled plugins. By default enable
vanilla, hdp and fake plugins. Fake plugin is needed for gate testing.

Change-Id: Ia557eafe19b7d8eb62b6511d8d5331a106ef4bc2
diff --git a/lib/sahara b/lib/sahara
index 64e82eb..55131f9 100644
--- a/lib/sahara
+++ b/lib/sahara
@@ -35,6 +35,8 @@
 
 SAHARA_AUTH_CACHE_DIR=${SAHARA_AUTH_CACHE_DIR:-/var/cache/sahara}
 
+SAHARA_ENABLED_PLUGINS=${SAHARA_ENABLED_PLUGINS:-vanilla,hdp,fake}
+
 # Support entry points installation of console scripts
 if [[ -d $SAHARA_DIR/bin ]]; then
     SAHARA_BIN_DIR=$SAHARA_DIR/bin
@@ -130,6 +132,8 @@
     iniset $SAHARA_CONF_FILE DEFAULT verbose True
     iniset $SAHARA_CONF_FILE DEFAULT debug $ENABLE_DEBUG_LOG_LEVEL
 
+    iniset $SAHARA_CONF_FILE DEFAULT plugins $SAHARA_ENABLED_PLUGINS
+
     iniset $SAHARA_CONF_FILE database connection `database_connection_url sahara`
 
     if is_service_enabled neutron; then