Bug 977275 - Add a horrible install-to-subdir hack in test manifests to support a goofy set of tests. r=gps

--HG--
rename : python/mozbuild/mozbuild/test/frontend/data/test-manifest-empty/moz.build => python/mozbuild/mozbuild/test/frontend/data/test-manifest-install-subdir/moz.build
rename : python/mozbuild/mozbuild/test/frontend/data/test-manifest-empty/empty.ini => python/mozbuild/mozbuild/test/frontend/data/test-manifest-install-subdir/subdir.ini
Bug 948801 - move browser-chrome tests in toolkit/mozapps/extensions/test/browser from Makefile.in to browser.ini. r=jmaher