iotop: Increase dd count to avoid occasional fails

On s390x there is no reccord of dd, I guess because it's done before it can
be recorded by iotop

-print log when test failed

tests/console/iotop.pm

@@ -26,13 +26,16 @@ sub run {
 
     # Test under load
     assert_script_run('(iotop -baoqn 10 > iotop.log &)');
-    assert_script_run("time dd if=/dev/zero of=./file.img bs=1k count=500000 status=none");
+    assert_script_run("time dd if=/dev/zero of=./file.img bs=1k count=2000000 status=none");
     assert_script_run("wait");
     assert_script_run("grep 'dd if=/dev/zero of=./file.img' iotop.log");
 
     # Cleanup
     assert_script_run("rm file.img iotop.log");
+}
 
+sub post_fail_hook {
+    assert_script_run("cat iotop.log");
 }
 
 1;