jenkins: add --enable-external-tests

Run the new logging_vty_test.vty VTY transcript test in our CI.

Change-Id: Ic4ec1f6c131da50b3956f16f0b49375f387196b3
diff --git a/contrib/jenkins_amd64.sh b/contrib/jenkins_amd64.sh
index c3af378..cd7b666 100755
--- a/contrib/jenkins_amd64.sh
+++ b/contrib/jenkins_amd64.sh
@@ -15,7 +15,8 @@
 
     prep_build "$src_dir" "$build_dir"
 
-    "$src_dir"/configure  --disable-silent-rules --enable-static $ENABLE_SANITIZE --enable-werror
+    "$src_dir"/configure  --disable-silent-rules --enable-static $ENABLE_SANITIZE --enable-werror \
+        --enable-external-tests
 
     run_make
 }