Bug 911055 - [Dialer]DuT doesn allow to dial a <<pause>>

We already have a mock for calls under ``shared/test/unit/mocks/dialer/mock_call.js``. You should use that one instead of reimplement it here. You need to preserve the ``TelephonyCall`` constructor though because that's needed by certain unit-tests. Create an empty object inside ``TelephonyCall`` and filling it with the contents of a ``MockCall`` object seems the easiest way to do this.