ConnectionService API has only one completed callback (1/3)

Refactor ConnectionService API so it has only one "completed"
callback, and connection state and failure codes indicates what
happened. Previous design where we had separate callbacks for failure,
cancellation and success was error prone because it was easy to forget
to implement one of them.

Bug: 16993846
Bug: 17070939

Change-Id: I84bf5d041cf78193ccf80db201b08db3b7014830