mslookup_client_mdns_test: disable by default

Only build and run the test, if --enable-mslookup-client-mdns-test is
passed to ./configure. Enable that option in jenkins.sh.

Related: OS#4385
Change-Id: Ie0cd4b0c55a1fbb00c215aeec7dcd0c15805add3
diff --git a/tests/testsuite.at b/tests/testsuite.at
index 827e9f8..d30b5e9 100644
--- a/tests/testsuite.at
+++ b/tests/testsuite.at
@@ -58,7 +58,9 @@
 AT_CHECK([$abs_top_builddir/tests/mslookup/mslookup_client_test], [0], [ignore], [experr])
 AT_CLEANUP
 
+# AT_SKIP_IF: disable without --enable-mslookup-client-mdns-test (OS#4385)
 AT_SETUP([mslookup_client_mdns])
+AT_SKIP_IF([! test -e $abs_top_builddir/tests/mslookup/mslookup_client_mdns_test ])
 AT_KEYWORDS([mslookup_client_mdns])
 cat $abs_srcdir/mslookup/mslookup_client_mdns_test.err > experr
 AT_CHECK([$abs_top_builddir/tests/mslookup/mslookup_client_mdns_test], [0], [ignore], [experr])