Revert "tests: qmp-test: verify command batching"

Revert "tests: qmp-test: verify command batching"

This reverts commit 91ad45061af0fe44ac5dadb5bedaf4d7a08077c8.

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 <[email protected]>
Message-Id: <20180323140821[email protected]>
Tested-by: Christian Borntraeger <[email protected]>
[eblake: reorder commits, enhance commit message]
Signed-off-by: Eric Blake <[email protected]>