openqa/worker: have swtpm service restart on success
    
    This is because swtpm is designed not to be persistent, it's
    sort of tied to a single "system" (VM in this case). We can't
    expect an instance will stick around after it's been "used", it
    doesn't do that, it exits successfully. So we need to restart it
    when that happens.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>