Remove Q_ASSERT's from qreadwritelock autotest

Remove Q_ASSERT's from qreadwritelock autotest

The tryWriteLock testfunction didn't do anything useful in non-debug
builds, due to the thread having the important code inside Q_ASSERT's,
which are no-ops in non-debug builds.  This commit removes the
Q_ASSERT's, counts the number of failures in the thread and fails the
test if there are any failures recorded.

Change-Id: I4750f66eeba22ab51ba348ebc06704052421f1ae
Task-number: QTBUG-17582
Reviewed-by: Rohan McGovern
(cherry picked from commit 00f724c943b83f10f9ca9475570708536947538e)