MBug#443092: test cases mysql and mysql_upgrade fails with wildcard DNS

When DNS is not working and returns some address even for non-existing
host names, some test cases fail with wrong error.

Fix by disabling these tests on such systems.

mysql-test/include/have_working_dns.inc

@@ -0,0 +1,11 @@
+#
+# Check if we have a working DNS.
+# Some 'wildcard dns' return some address even for non-existing hosts. This
+# makes it hard to test connections to such host names.
+# The actual check for working DNS is done in Perl, and the result available
+# in an environment variable.
+#
+--require r/have_working_dns.require
+disable_query_log;
+eval SELECT LENGTH('$HAVE_BROKEN_DNS') = 0 AS 'have_working_dns';
+enable_query_log;