restapi: Expose vm.auto_converge and vm.migrate_compressed properties

  <vm>
    <migration>
      <auto_converge>true|false|inherit</auto_converge>
      <compressed>true|false|inherit</compressed>
    </migration>
  </vm>

And similarly for <cluster>

Change-Id: I9161896d1709c7492201667aa2c5955c5e37efd0
Signed-off-by: Martin Betak <mbetak@redhat.com>
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1151001