Enable integration with hooks on a failed update.

Adding support for err hooks when update is rolled back or failed. Hooks use thrift ResponseCode to detect operation failure, so updater has to simulate an ERROR response code to properly support error hooks.

Also, failed_instances no longer tell the truth as far as update status goes. Converted to use failure count check to determine update success.

Testing Done:
./pants src/test/python/twitter/aurora/client/api:all

Reviewed at https://reviews.apache.org/r/16139/