refactor(test): rename test_lib to testing

Old test_lib is now testing_internal
test_lib_public is now testing

modules/angular2/testing_internal.ts

@@ -0,0 +1,6 @@
+// Test library and utilities for internal use.
+export * from './src/testing/testing_internal';
+export * from './src/testing/test_component_builder';
+export * from './src/testing/test_injector';
+export * from './src/testing/fake_async';
+export * from './src/testing/utils';