Description of problem:
qemu-kvm-ma block jobs are all disabled, but transaction still available to create live snapshot and live backup.

Version-Release number of selected component (if applicable):
qemu-kvm-ma-10:2.10.0-6.el7

How reproducible:
100%

Steps to Reproduce:
1. Launch guest
2. Perform live snapshot or live backup by transaction:

{'execute': 'transaction', 'arguments': {'actions': [{'data': {'device':'drive_image1', 'snapshot-file': '/home/image1-snap', 'mode': 'absolute-paths', 'format': 'qcow2'}, 'type': 'blockdev-snapshot-sync'}]}}

{'execute': 'transaction', 'arguments': {'actions': [{'data': {'device':'drive_image1', 'target':'test.img', 'mode': 'absolute-paths', 'format': 'qcow2','sync':'full'}, 'type': 'drive-backup'}]}}


Actual results:
Block job success.
{"timestamp": {"seconds": 1511754423, "microseconds": 723426}, "event": "BLOCK_JOB_COMPLETED", "data": {"device": "drive_image1", "len": 21474836480, "offset": 21474836480, "speed": 0, "type": "backup"}}

Expected results:
It should be forbidden. 

Additional info:
qemu-kvm-2.9.0-23.el7a.ppc64le has the issue too.