This adds a flag to |mach robocop| that does everything to run a
Robocop test except launch the actual test. Instead of launching the
test, it starts the mochi.test server and launches Fennec with a test
profile; then it sits and waits forever.
This allows regular Java IDEs (IntelliJ, but previously Eclipse) to
run Robocop tests like regular instrumentation tests, "injecting" them
into the prepared testing environment. It's quite nice!
