qga: added empty qmp_quest_get_fsinfo functionality.

qga: added empty qmp_quest_get_fsinfo functionality.

We need qmp_quest_get_fsinfo togather with vss-provider, which works with
volumes. The call to this function is implemented via
FindFirst/NextVolumes. Moreover, volumes in Windows OS are filesystem unit,
so it will be more effective to work with them rather with devices.

Signed-off-by: Olga Krishtal <okrishtal@virtuozzo.com>
Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: Eric Blake <eblake@redhat.com>
CC: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>