Add is_ubuntu function

This replaces all of the [[ "$os_PACKAGE" = "deb" ]] tests, except when
those tests are before straight calls to dpkg.

Change-Id: I8a3ebf1b1bc5a55d736f9258d5ba1d24dabf04ea
diff --git a/lib/cinder b/lib/cinder
index 1aa34cd..ce160bf 100644
--- a/lib/cinder
+++ b/lib/cinder
@@ -237,7 +237,7 @@
 # start_cinder() - Start running processes, including screen
 function start_cinder() {
     if is_service_enabled c-vol; then
-        if [[ "$os_PACKAGE" = "deb" ]]; then
+        if is_ubuntu; then
             _configure_tgt_for_config_d
             if [[ ! -f /etc/tgt/conf.d/cinder.conf ]]; then
                echo "include $CINDER_STATE_PATH/volumes/*" | sudo tee /etc/tgt/conf.d/cinder.conf