pm-utils: do not leave background tasks - will be killed by systemd

qvm-sync-clock running in background is killed as soon as
qubes-suspend.service is terminated.
Additionally restore --verbose option, which was the case (implicitly)
in previous qvm-run based code.

Fixes QubesOS/qubes-issues#1795

pm-utils/01qubes-sync-vms-clock

@@ -3,7 +3,7 @@
 sync_qubes_vms_wallclock()
 {
     # Sync all VMs (based on dom0 clock if network time sync fails)
-    /usr/bin/qvm-sync-clock --force &
+    /usr/bin/qvm-sync-clock --force --verbose
 }
 
 case "$1" in