blktapctrl: Fix too early close of pipes

blktapctrl: Fix too early close of pipes

Connections to ioemu have single_handler set, so they are closed as
soon as all images of a certain type are closed. This is wrong with
ioemu: All images that belong to the same domain are handled by the
same backend process (usually qemu-dm, but also tapdisk-ioemu for
domains without device model), regardless of the image type.

This patch checks for the same-domain condition for ioemu connections.

Signed-off-by: Kevin Wolf <kwolf@suse.de>