add log entry when hivemind got 'wait_for_haf' stage
Because hivemind suffers for #258 it is required to support 'wait_for_haf' stage in Python code, now when hivemind starts waiting for haf we got in log:
INFO - hive.indexer.sync:107 - Switched to `wait_for_haf` mode | block: 0 | processing time: 00s
INFO - hive.indexer.sync:123 - Last imported block is: 0
INFO - hive.indexer.sync:123 - Last imported block is: 0
requires: haf!583 (merged)