Reduce the runtime of tst_selftests

The addition of testing for multiple loggers greatly increased the total
runtime of this test, in fact making it the slowest testcase in Qt.
Fortunately this is only due to a couple of slow subtests whose behavior
is unlikely to be affected by the loggers.  Change it to run these slow
subtests just for a couple of loggers, instead of all the combinations.

Change-Id: Ie90f6c0ca29470ed6a7c4e2e185f852602a2d162
Reviewed-by: Jason McDonald <jason.mcdonald@nokia.com>

tests/auto/testlib/selftests/tst_selftests.cpp

@@ -395,6 +395,12 @@ void tst_Selftests::runSubTest_data()
                 if (subtest == "float") {
                     continue;
                 }
+                // these tests are quite slow, and running them for all the loggers significantly
+                // increases the overall test time.  They do not really relate to logging, so it
+                // should be safe to run them just for the stdout loggers.
+                if (subtest == "benchlibcallgrind" || subtest == "sleep") {
+                    continue;
+                }
             }
 
             QTest::newRow(qPrintable(QString("%1 %2").arg(subtest).arg(loggerSet.name)))