Fail at first boot if time can't be synced

Fail at first boot if time can't be synced for some reasons.  It's
better to fail here than laster on because keystone can't authenticate
at the end of the deployment.

Change-Id: Ib4c139c76959271f12e795a7eef13e52dd0782d7

firstboot/userdata_timesync.yaml

@@ -71,7 +71,7 @@ resources:
         str_replace:
           template: |
             #!/bin/bash
-            set -x
+            set -xe
             if [ "$service" = "chrony" ]; then
                 if command -v chronyc >/dev/null; then
                     chronyc makestep