tests: Add qemu test for multiple timers
    
    The following XML is the recommended default clock configuration for
    qemu:
    
      <clock offset='utc'>
        <timer name='rtc' tickpolicy='catchup'/>
        <timer name='pit' tickpolicy='delay'/>
        <timer name='hpet' present='no'/>
      </clock>
    
    However we weren't testing any of those timer elements.