vdsm: Add force and timeout options to VM.shutdown

Added optional parameters 'timeout' and 'force' to
shutdown in vdsm and vdsClient.

Timeout represents number of seconds to wait before falling back to next
alternative method of shutdown/reboot.

If 'force' is True and all graceful methods fail, we reset/destroy the VM.

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1054070
Change-Id: I30180f9906eb45fa485aa7d773a436e62bd3c815
Signed-off-by: Martin Betak <mbetak@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/27054
Reviewed-by: Francesco Romani <fromani@redhat.com>
Reviewed-by: Vinzenz Feenstra <vfeenstr@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>