input-linux: initialize key state

Query input device keys, initialize state accordingly, so the correct
state is reflected in case any key is pressed at initialization time.
There is a high chance for this to actually happen for the 'enter' key
in case you start qemu with a terminal command (directly or virsh).

When finding any pressed keys the input grab is delayed until all keys
are lifted, to avoid confusing guest and host with appearently stuck
keys.

Reported-by: Muted Bytes <mutedbytes@gmail.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-id: 1476277384-30365-1-git-send-email-kraxel@redhat.com