[autotests] tst_qscroller fails too often in CI

The tst_qscroller autotest has failed 18 times in CI between 2013-01-18 and 2013-02-25, and ranks as the third most failing test in that time frame. It seems likely that the test needs a rewrite.
Example of failure: http://lists.qt-project.org/pipermail/ci-reports/2013-January/003431.html