Enhance load testing tools to be able to initiate webrtc calls towards restcomm (using registrarless)

[atsakiridis]

Right now we only support receiving calls originating at restcomm, which typically are initiated by sipp. The problem with receiving calls is that the scenario is more complicated and easier to break. Contributing factors:

• Registrations add more load to restcomm and aren't essential to the test at hand which is to load test MS
• Complex setup. We need to:
  1. provision/unprovision restcomm clients for each registering client
  2. provision/unprovision external service to properly distribute calls amongst all clients
  3. have external service in place to feed RCML to Restcomm
• More complex runtime. For this to work with 50 concurrent calls, we need to actually spawn more browsers so that there's a 'padding' of outstanding browsers ready to handle calls until new are spawned. In my tests I've seen that for safe tests we need 2X concurrent calls (i.e. 100 browsers in the scenario above)

[atsakiridis]

Missed some impacts on restcomm-test.py