blktap: Fix qcow2raw.

blktap: Fix qcow2raw.

qcow2raw would hang the conversion just short of 100%, because the
final write queue was never being submitted.  If a blktap drivers read
synchronously, then "submit_events" and "complete" variables are
checked before getting set, so the fact that reads have finished is
not noticed, so the final write queue was never submitted.

Note that I have also removed the variables write_complete and
read_complete.  They were unused, and they were also not set correctly
in the synchronous case.

Signed-off-by: Charles Coffing <ccoffing@novell.com>