error: Link qemu-img, qemu-nbd, qemu-io with qemu-error.o

error: Link qemu-img, qemu-nbd, qemu-io with qemu-error.o

The location tracking interface is used by code shared with qemi-img,
qemu-nbd and qemu-io, so it needs to be available there.  Commit
827b0813 provides it in a rather hamfisted way: it adds a dummy
implementation to qemu-tool.c.

It's cleaner to provide the real thing, and put a few more dummy
monitor functions into qemu-tool.c.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>