Clarified the error message printed when mtr's test cleanup check fails.

	  # Test failed, grab the report mysqltest has created

	  my $report= mtr_grab_file($err_file);

	  $tinfo->{check}.=

	    "\nThe check of testcase '$tname' failed, this is the\n".

	      "diff between before and after:\n";

	    "\nMTR's internal check of the test case '$tname' failed.

This means that the test case does not preserve the state that existed

before the test case was executed.  Most likely the test case did not

do a proper clean-up.

This is the diff of the states of the servers before and after the

test case was executed:\n";

	  $tinfo->{check}.= $report;

	  # Check failed, mark the test case with that info