Handle Xen 4.3 states better

Handle Xen 4.3 states better

In Xen commit e1475a6693aac8cddc4bdd456548aa05a625556b, the output from
xl list was extended to provide a reason for shutdowns. This breaks
our somewhat strict parsing of the output in certain situations where
the new states appear (e.g. the short suspension during a migration, or
an instance reboot).

This patch makes sure the new states (barring the mysterious watchdog
state) are handled correctly.

Signed-off-by: Hrvoje Ribicic <riba@google.com>
Reviewed-by: Klaus Aehlig <aehlig@google.com>