qunit: Implement suppressWarnings/restoreWarnings

There are various tests triggering deprecation warnings because
they are testing deprecated functionality, on purpose.

Surpress these so that the logs aren't filled with false
positives in Jenkins.

Change-Id: I4bb546781a0c89999b2e5df7715abf492a44856d
Merge "qunit: Implement suppressWarnings/restoreWarnings"