Improve a check in bonding_conf_consistency test

[Sergey Novikov]

Sometimes test "bonding_conf_consistency" fails due to the assertion https://github.com/openstack/fuel-qa/blob/stable/mitaka/fuelweb_test/tests/test_bonding.py#L526

we need to improve this check for case if cluster is partially deployed. in the case task "deployment" has status "ready", but there is failed task on some nodes

The second way to fix this bug, improve the following part of the code https://github.com/openstack/fuel-qa/blob/stable/mitaka/fuelweb_test/tests/test_bonding.py#L507-L522 . A new implementation must ensure determined result