Remove Q_ASSERT from QThread autotest

Report a meaningful fatal error instead of aborting in debug mode builds
and failing silently in release mode builds.

Change-Id: If9a6c0655e021b3bb6b7d894aefd9bbcc58e4605
Task-number: QTBUG-17582
Reviewed-by: Rohan McGovern
(cherry picked from commit fed42f25e129af1f4f2c03a075530ad7111d2fdd)

tests/auto/qthread/tst_qthread.cpp

@@ -209,7 +209,7 @@ public:
             cond.wait(&mutex, five_minutes);
         }
         setTerminationEnabled(true);
-        Q_ASSERT_X(false, "tst_QThread", "test case hung");
+        qFatal("tst_QThread: test case hung");
     }
 };