ktest.pl: Kill test if mailer is not supported

If the user specifies a MAILTO, but the MAILER is not supported, then
kill the test.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

tools/testing/ktest/ktest.pl

@@ -4168,7 +4168,7 @@ sub send_email {
 	}
         if ($mailer eq "mail" || $mailer eq "mailx"){ _mailx_send(@_);}
         elsif ($mailer eq "sendmail" ) { _sendmail_send(@_);}
-        else { doprint "\nYour mailer: $mailer is not supported.\n" }
+        else { die "\nYour mailer: $mailer is not supported.\n" }
     }
 }