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.