Mitigate issues with stuck calls blocking new outgoing calls.

There are edge cases where a call can get stuck in a "connecting" state.
When this occurs it is no longer possible to place an outgoing calls.
As a mitigation, attempt to disconnect a stuck "connecting" call so
that a new outgoing call can be placed.

Test: add unit test coverage for this case.
Test: manual test with test connection service.
Fixes: 180154311
Change-Id: Ifb717347e1bf7bb289a9b0198ab99a6b459e1cd9