move all plugin tests out of babel-core and into their appropriate folders

packages/babel-plugin-transform-runtime/test/fixtures/runtime/modules/actual.js

@@ -0,0 +1,2 @@
+import foo from "bar";
+foo;

packages/babel-plugin-transform-runtime/test/fixtures/runtime/modules/expected.js

@@ -0,0 +1,9 @@
+"use strict";
+
+var _bar = require("bar");
+
+var _bar2 = _interopRequireDefault(_bar);
+
+function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }
+
+_bar2.default;

packages/babel-plugin-transform-runtime/test/fixtures/runtime/modules/options.json

@@ -0,0 +1,3 @@
+{
+  "plugins": ["transform-runtime", "transform-es2015-modules-commonjs"]
+}