qunit macro: Invoke grunt without --verbose

With --verbose there's a lot of output *after* the results of the
(potentially) failed tests. Enough that the test results are often
not in the short view of the Jenkins build console.

The verbose output isn't all that useful anyway (more for debugging
of Grunt than the QUnit tests).

Bug: T63843
Change-Id: I138d90df05eca7820cb3b066b476fb822f98b46d