build(integration): fix tests (#14371)

Previously, the `integration/` tests were failing, because `concurrently "foo"`
does not inherit the `PATH` env var ([more info][1]).

This commit fixes it, by setting the `PATH` env var explicitly:
`concurrently "PATH=$PATH foo"`.

This commit also includes some minor refactoring of the `integration/` tests scripts:

- Move build-related operations to `ci-lite/build.sh` (for consistency).
- Use `yarn run ...` instead of `npm run ...` inside package.json scripts.
- Use global `yarn` (since we are already using it for `aio/`).
- Fix some `travis_fold` statements.

[1]: https://github.com/kimmobrunfeldt/concurrently/issues/61#issuecomment-252081610

integration/hello_world__closure/package.json

@@ -23,7 +23,7 @@
     "protractor": "file:../../node_modules/protractor"
   },
   "scripts": {
-    "test": "ngc && ./bundle.sh && concurrently \"npm run serve\" \"npm run protractor\" --kill-others --success first",
+    "test": "ngc && ./bundle.sh && concurrently \"PATH=$PATH yarn run serve\" \"PATH=$PATH yarn run protractor\" --kill-others --success first",
     "serve": "lite-server -c e2e/browser.config.json",
     "preprotractor": "tsc -p e2e",
     "protractor": "protractor e2e/protractor.config.js"