libxl_qmp: Tell QEMU about live migration or snapshot

libxl_qmp: Tell QEMU about live migration or snapshot

Since version 2.10, QEMU will lock the disk images so a second QEMU
instance will not try to open it. This would prevent live migration from
working correctly. A new parameter as been added to the QMP command
"xen-save-devices-state" in QEMU version 2.11 which allow to unlock the
disk image for a live migration, but also keep it locked for a snapshot.

QEMU commit: 5d6c599fe1d69a1bf8c5c4d3c58be2b31cd625ad
"migration, xen: Fix block image lock issue on live migration"

The extra "live" parameter can only be use if QEMU knows about it, so
only add it if qemu is recent enough.

The struct libxl__domain_suspend_state as now knowledge if the suspend
is part of a live migration.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>