move horizon logic to lib to clean up stack.sh

pre holiday refactor extrodinare, get the horizon code
over fully into lib/horizon so that all these fixes aren't
scattered through stack.sh

Change-Id: I7f26c5c6708d5693048eb7b1ce792122adbc7351
diff --git a/unstack.sh b/unstack.sh
index 1a2cad8..0040cf1 100755
--- a/unstack.sh
+++ b/unstack.sh
@@ -26,6 +26,7 @@
 
 # Get project function libraries
 source $TOP_DIR/lib/cinder
+source $TOP_DIR/lib/horizon
 
 # Determine what system we are running on.  This provides ``os_VENDOR``,
 # ``os_RELEASE``, ``os_UPDATE``, ``os_PACKAGE``, ``os_CODENAME``
@@ -51,7 +52,7 @@
 
 # Apache has the WSGI processes
 if is_service_enabled horizon; then
-    stop_service apache2
+    stop_horizon
 fi
 
 SCSI_PERSIST_DIR=$CINDER_STATE_PATH/volumes/*