Rename service.Application.stopTestChan to service.Application.stopChan

[eddyleelin]

As @tigrannajaryan mentioned in the previous issue #2260,

We should... rename stopTestChan to just stopChan. I can't see anything special about this stopping that is only applicable to tests. It is just a way to stop the service.

Originally posted by @tigrannajaryan in #2260 (comment)

If this is a valid issue, I could take this one on! Thanks.