Unlike test-blockjob-txn, QMP releases the reference to the transaction
before the jobs finish.  Thus, qemu-iotest 124 showed a failure while
working on the next patch that the unit tests did not have.  Make
the test a little nastier.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 20170508141310.8674-10-pbonzini@redhat.com
Signed-off-by: Jeff Cody <jcody@redhat.com>