Add is_fedora and exit_distro_not_supported functions

Between is_fedora, is_ubuntu and is_suse, we can make the code a bit
simpler to read. We also use exit_distro_not_supported to identify
places where we need implementation details for new distros.

As "/sbin/service --skip-redirect" is Fedora-specific, guard this with a
is_fedora test too.

Change-Id: Ic77c0697ed9be0dbb5df8e73da93463e76025f0c
diff --git a/lib/cinder b/lib/cinder
index 9b9d50d..a43f0a1 100644
--- a/lib/cinder
+++ b/lib/cinder
@@ -195,8 +195,8 @@
         mkdir -p $CINDER_STATE_PATH/volumes
 
         if sudo vgs $VOLUME_GROUP; then
-            if [[ "$os_PACKAGE" = "rpm" ]]; then
-                # RPM doesn't start the service
+            if is_fedora || is_suse; then
+                # service is not started by default
                 start_service tgtd
             fi
 
@@ -245,9 +245,15 @@
             # do it in two steps
             sudo stop tgt || true
             sudo start tgt
-        else
+        elif is_fedora; then
             # bypass redirection to systemctl during restart
             sudo /sbin/service --skip-redirect tgtd restart
+        elif is_suse; then
+            restart_service tgtd
+        else
+            # note for other distros: unstack.sh also uses the tgt/tgtd service
+            # name, and would need to be adjusted too
+            exit_distro_not_supported "restarting tgt"
         fi
     fi