Create a "wait for selector with text" function for E2E test

In some of our E2E test, we use `page.waitForSelector` with a `text` option (ie. https://github.com/Automattic/woocommerce-services/blob/develop/tests/e2e-tests/specs/admin/create-shipping-label.test.js#L36). The idea is to wait for this selector and regex the `text` if there are more than one selector that matches. However, `waitForSelector` doesn't take `text` as an option https://github.com/puppeteer/puppeteer/blob/master/docs/api.md#pagewaitforselectorselector-options.

The library that takes a `text` option is https://github.com/smooth-code/jest-puppeteer/tree/master/packages/expect-puppeteer#api but none of these seem to do a `waitForSelector`.

We can do something similar to what this function does: https://github.com/Automattic/woocommerce-services/blob/e620088715377e85c77308d1877f1c066c847c47/tests/e2e-tests/specs/admin/shipping-settings.test.js#L19-L25

**Output**
- Create this function and put it inside our `utils/`
- Replace `create-shipping-label.test.js` to use this function
- Replace `shipping-settings.test.js` to use this function
- All test pass locally and on Travis

Start by reading the existing selector-and-text logic in tests/e2e-tests/specs/admin/shipping-settings.test.js and the related usage in create-shipping-label.test.js. Add the shared function under utils/, update both E2E tests to use it, and run the E2E suite to confirm all tests pass locally and on Travis.

Written by the indexing model from the issue text.