fix build issue
- fix indexer/cluster_manager_agent.go due to index manager API changes

Change-Id: I7b81f5be877adf57a54243c4e210de97364a33c3
Reviewed-on: http://review.couchbase.org/44148
Reviewed-by: John Liang <johliang00@gmail.com>
Tested-by: John Liang <johliang00@gmail.com>