jamiaccount: do not stop all subcall if one fails

+ In jamiaccount, if a requestSIPConnection was failing, all subcalls
were stopped causing the main call to fail if not connected. In this
patch we only stop the subcall linked to that request.
+ In connectionmanager, if a request failed, we stopped all other
connections instead of just using the id of the request.

This fix calls whenever somebody called a contact right after the
contact changed its connectivity (and the keep-alive is not sent).

Change-Id: I0d9b14795aad37363de992cb29d4d4ca44668285