[Bug 31784] New: Add support for VM snapshots

http://bugs.winehq.org/show_bug.cgi?id=31784

Bug #: 31784
           Summary: Add support for VM snapshots
           Product: Wine-Testbot
           Version: unspecified
          Platform: x86
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: unknown
        AssignedTo: [e-mail]
        ReportedBy: [e-mail]
    Classification: Unclassified

As we expand the number of configurations to test it seems wasteful to have to
create and maintain a brand new VM just for them. In a lot of cases all we need
is to slightly reconfigure a VM to add a CD image, add network interfaces or
change the locale and run the test with these changes settings.

That's where snapshots can be useful: take a snapshot for each configuration we
need to test and then let the TestBot start the VM from the right snapshot.

There is a catch though: while it's possible to run the tests in two VMs in
parallel, for a given VM only one snapshot can be active at a time. There's two
consequences:
* TestBot must know about snapshot and not try to simultaneously run the tests
in two snapshots belonging to the same VM.
* If in the base configurations (those all Wine patches run on) we have a VM
with ten snapshots, it means we will need to run the tests ten times
*sequentially*. That VM is quickly going to become a bottleneck. So we should
still limit the number of snapshots per VM, at least in the base
configurations.