Make tst_QTemporaryFile::fileTemplate() more informative on failure

A QCOMPARE(..., true) isn't much use; and failure would have set the
object's .errorString(), which seems like it'd be worth reporting, so
use QVERIFY2() instead.

Change-Id: I2f3f9379984694891de81d2ffebc696d91eec70f
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

tests/auto/corelib/io/qtemporaryfile/tst_qtemporaryfile.cpp

@@ -215,7 +215,7 @@ void tst_QTemporaryFile::fileTemplate()
     if (!fileTemplate.isEmpty())
         file.setFileTemplate(fileTemplate);
 
-    QCOMPARE(file.open(), true);
+    QVERIFY2(file.open(), qPrintable(file.errorString()));
 
     QString fileName = QFileInfo(file).fileName();
     if (prefix.length())