iotests/185: Add post-READY quit tests

iotests/185: Add post-READY quit tests

185 tests quitting qemu while a block job is active.  It does not
specifically test quitting qemu while a mirror or active commit job is
in its READY phase.

Add two test cases for this, where we respectively mirror or commit to
an external QSD instance, which provides a throttled block device.  qemu
is supposed to cancel the job so that it can quit as soon as possible
instead of waiting for the job to complete (which it did before 6.2).

Signed-off-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20220303164814.284974-5-hreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>