Let's lint the app/test/ files

This should pass Travis since we're still excluding the app/tests/** via Grunt [/grunttasks/jshint.js:25](https://github.com/mozilla/fxa-content-server/blob/master/grunttasks/jshint.js#L25) task.
Remove the `'!<%= yeoman.app %>/tests/**'` line (and preceeding comma) and you should see the following errors when running `$ grunt lint`:

```
    Running "jshint:app" (jshint) task

    app/tests/mocks/window.js
      line 55   col 54  'bubbles' is defined but never used.
      line 63   col 28  'y' is defined but never used.
      line 63   col 25  'x' is defined but never used.
      line 66   col 46  'timeoutMS' is defined but never used.
      line 66   col 35  'callback' is defined but never used.
      line 75   col 36  'timeout' is defined but never used.

    app/tests/spec/lib/channels/web.js
      line 14   col 13  'assert' is defined but never used.
      line 13   col 49  'afterEach' is defined but never used.

    app/tests/spec/lib/fxa-client.js
      line 422  col 13  'done' is not defined.
      line 207  col 35  'info' is defined but never used.
      line 209  col 31  'err' is defined but never used.
      line 402  col 35  'complete' is defined but never used.

    app/tests/spec/lib/session.js
      line 13   col 49  'beforeEach' is defined but never used.
      line 13   col 49  'afterEach' is defined but never used.

    app/tests/spec/lib/translator.js
      line 51   col 53  ['Show'] is better written in dot notation.
      line 65   col 55  ['Show'] is better written in dot notation.

    app/tests/spec/lib/url.js
      line 16   col 14  'channel' is defined but never used.
      line 14   col 34  'Constants' is defined but never used.

    app/tests/spec/lib/validate.js
      line 16   col 14  'channel' is defined but never used.

    app/tests/spec/lib/xss.js
      line 16   col 14  'channel' is defined but never used.

    app/tests/spec/views/button_progress_indicator.js
      line 13   col 49  'afterEach' is defined but never used.

    app/tests/spec/views/complete_reset_password.js
      line 240  col 55  'email' is defined but never used.

    app/tests/spec/views/confirm.js
      line 49   col 26  'routerMock' is not defined.

    app/tests/spec/views/force_auth.js
      line 20   col 20  'wrapAssertion' is defined but never used.

    app/tests/spec/views/pp.js
      line 18   col 21  'router' is defined but never used.

    app/tests/spec/views/settings.js
      line 19   col 20  'wrapAssertion' is defined but never used.

    app/tests/spec/views/tos.js
      line 37   col 7   Unreachable 'assert' after 'return'.
      line 18   col 21  'router' is defined but never used.

    ✖ 28 problems

    Warning: Task "jshint:app" failed. Use --force to continue.

    Aborted due to warnings.    Running "jshint:app" (jshint) task

    app/tests/mocks/window.js
      line 55   col 54  'bubbles' is defined but never used.
      line 63   col 28  'y' is defined but never used.
      line 63   col 25  'x' is defined but never used.
      line 66   col 46  'timeoutMS' is defined but never used.
      line 66   col 35  'callback' is defined but never used.
      line 75   col 36  'timeout' is defined but never used.

    app/tests/spec/lib/channels/web.js
      line 14   col 13  'assert' is defined but never used.
      line 13   col 49  'afterEach' is defined but never used.

    app/tests/spec/lib/fxa-client.js
      line 422  col 13  'done' is not defined.
      line 207  col 35  'info' is defined but never used.
      line 209  col 31  'err' is defined but never used.
      line 402  col 35  'complete' is defined but never used.

    app/tests/spec/lib/session.js
      line 13   col 49  'beforeEach' is defined but never used.
      line 13   col 49  'afterEach' is defined but never used.

    app/tests/spec/lib/translator.js
      line 51   col 53  ['Show'] is better written in dot notation.
      line 65   col 55  ['Show'] is better written in dot notation.

    app/tests/spec/lib/url.js
      line 16   col 14  'channel' is defined but never used.
      line 14   col 34  'Constants' is defined but never used.

    app/tests/spec/lib/validate.js
      line 16   col 14  'channel' is defined but never used.

    app/tests/spec/lib/xss.js
      line 16   col 14  'channel' is defined but never used.

    app/tests/spec/views/button_progress_indicator.js
      line 13   col 49  'afterEach' is defined but never used.

    app/tests/spec/views/complete_reset_password.js
      line 240  col 55  'email' is defined but never used.

    app/tests/spec/views/confirm.js
      line 49   col 26  'routerMock' is not defined.

    app/tests/spec/views/force_auth.js
      line 20   col 20  'wrapAssertion' is defined but never used.

    app/tests/spec/views/pp.js
      line 18   col 21  'router' is defined but never used.

    app/tests/spec/views/settings.js
      line 19   col 20  'wrapAssertion' is defined but never used.

    app/tests/spec/views/tos.js
      line 37   col 7   Unreachable 'assert' after 'return'.
      line 18   col 21  'router' is defined but never used.

    ✖ 28 problems

    Warning: Task "jshint:app" failed. Use --force to continue.

    Aborted due to warnings.
```

We can merge this beast and start a separate PR for addressing unused variables and the few other remaining issues. For things like "better written in dot notation" we can have JSHint ignore those lines or selectively disable that rule for those few lines of select code.