Post Config API block until timeoutUpdateReached

Due to a blocking chan http post (update) config api doesn't work.
It seems that code is written to make tests working.
I don't understand this part of code:
https://github.com/influxdata/kapacitor/blob/master/services/config/service.go#L261-L282

Start by reading services/config/service.go around lines 261-282, then trace the blocking channel used by the HTTP POST config update and how timeoutUpdateReached is involved. Reproduce the reported behavior and determine what completion condition the API should use; done means the POST config API no longer blocks unexpectedly while the relevant timeout behavior remains covered.

Written by the indexing model from the issue text.