Revert "tests: qmp-test: add oob test"

This reverts commit d003f7a8.

Enabling OOB caused several iotests failures; due to the imminent
2.12 release, the safest action is to disable OOB, but first we
have to revert tests that rely on OOB.

Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20180323140821.28957-3-peterx@redhat.com>
Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
[eblake: reorder commits, enhance commit message]
Signed-off-by: Eric Blake <eblake@redhat.com>