This patch on its own will break mach. Part 3 will refactor mach's
loader to discover and load modules using a modified module finding
method.
--HG--
rename : python/mach/mach/settings.py => python/mach/mach/commands/settings.py
rename : python/mach/mach/build.py => python/mozbuild/mach/commands/build.py
rename : python/mach/mach/testing.py => python/mozbuild/mach/commands/testing.py
rename : python/mach/mach/warnings.py => python/mozbuild/mach/commands/warnings.py