Bug 818819 - Revamp mach's interaction with mochitests; r=Ms2ger

mach now invokes mochitests using the native Python API (as opposed to
make targets). mach now supports --shuffle, --rerun-failures,
--keep-open, --no-autorun, --repeat, and --slow.
Bug 854921 - Pass firefox path to metrotestharness so tests.ini can be written to a location that works with test zips / test slaves. Also add metro tests to mochitest tests.jar. r=mbrubeck, bbondy
Bug 833016 - Fix for FrameworkView addrefing which is causing crashes on shutdown. r=bbondy