[autotests] tst_qclipboard fails too often in CI

The tst_qclipboard autotest has failed 16 times in CI between 2013-01-18 and 2013-02-25, and ranks as the fourth 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/002720.html