[PVE-User] vzdump backups are randomlingly failing

[Dietmar Maurer]

> I'm having trouble (randomly) while backing up VMs with the following error:
> 
> 616: Oct 24 01:29:49 INFO: Starting Backup of VM 616 (qemu)
> 616: Oct 24 01:29:49 INFO: status = running
> 616: Oct 24 01:29:50 INFO: backup mode: suspend
> 616: Oct 24 01:29:50 INFO: ionice priority: 7
> 616: Oct 24 01:29:51 INFO: suspend vm
> 616: Oct 24 01:29:52 INFO: trying to aquire lock... failed

Another vzdump is already running.