qga-win: Updating guest_set_time action

  At the moment, Windows libraries don't provide a way to access
  RTC, so, a workaround is to use the Windows w32tm command to
  resync the time.
  Related bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1183874

Signed-off-by: Bishara AbuHattoum <bishara@daynix.com>
Reviewed-by: Sameeh Jubran <sameeh@daynix.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
