BSN: Set inconsistency record on delete failure

Set a bad value in the consistency DB on a delete
failure so a sync is triggered the next time the backend
servers become available.

This fixes the issue where the backend servers are unavailable
when an object is deleted from ML2 but not deleted from the
backend.

Conflicts:

	neutron/tests/unit/bigswitch/test_servermanager.py

Closes-Bug: #1377350
Change-Id: I24713a03af4d3499645241f900de1f572689c235
Merge branch 'stable/icehouse' of github.com:bigswitch/neutron into bs_icehouse