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 <[email protected]>
Signed-off-by: Denis V. Lunev <[email protected]>
CC: Eric Blake <[email protected]>
CC: Michael Roth <[email protected]>
Signed-off-by: Michael Roth <[email protected]>