Removed "use diagnostics", reduces Perl speed significantly. Can be
  enabled with "perl -Mdiagnostics mysql-test-run.pl".
mtr_report.pl:
  Don't try output "skipped" comment if there is none (bug#24471)


mysql-test/mysql-test-run.pl:
  Removed "use diagnostics", reduces Perl speed significantly. Can be
  enabled with "perl -Mdiagnostics mysql-test-run.pl".
mysql-test/lib/mtr_report.pl:
  Don't try output "skipped" comment if there is none (bug#24471)