886 | BUG: Ringing status shouldn't set Verboice disposition to UNKNOWN

https://trello.com/c/3Kpp4ITB

Because the busy status sometimes is delivered before ringing, a ringing status
resets the "busy" disposition to an unknown disposition. Instead, the disposition
should be set to unknown when making a call, and ringing does not change the disposition.

Change-Id: I70e0de53ac804af53d2cc5da4ecb1601947e6816
Merge "886 | BUG: Ringing status shouldn't set Verboice disposition to UNKNOWN"