add make target for gaia-integration device testing

Currently, we have to use runner_service to kick off gaia-integration tests on devices/emulator. This patch lets use use the 'make test-integration' target for gaia integration tests on any platform (desktop, device, emulator). By default, it assumes 'desktop'. 

If something other than desktop is used, then we change the default values of REPORTER and MARIONETTE_RUNNER_HOST to those needed by devices/emulators. bin/gaia-marionette has been updated to kick off the runner_service's listener process (a python script used to interface with devices/emulators) and will kill that process when any kill/interrupt signal is received or when the script is complete.

This also removes the gaia-marionette call from runner-service.

NOTE: if you Cmd+C or Ctrl+C during a device test, you'll see ^C in the stdout, and it may look like nothing is happening for a while, but that's because mocha has received your abort signal, and will only propagate it once its next event gets processed. This actually happens now with the desktop, but since desktop is faster, you don't really notice it as often. On device, aborting during some actions will take a while, like if you do this while the phone is rebooting, for example. In this case, it's easier to Cmd+Z/Ctrl+Z, which will kill everything quickly.
same