Remove unstable connectors from downstream list

Configure cis-jenkins CI build to ignore the following repositories
when deciding which downstream projects to build:

 - loopback-connector-db2z
 - loopback-connector-informix
 - loopback-connector-mqlight
 - loopback-connector-kv-extreme-scale

The list is the same as we have in loopback-datasource-juggler now.

Signed-off-by: Miroslav Bajtoš <mbajtoss@gmail.com>

package.json

@@ -38,5 +38,13 @@
     "eslint-config-loopback": "^13.1.0",
     "loopback-datasource-juggler": "^3.32.0",
     "mocha": "^6.2.0"
+  },
+  "ci": {
+    "downstreamIgnoreList": [
+      "loopback-connector-db2z",
+      "loopback-connector-informix",
+      "loopback-connector-mqlight",
+      "loopback-connector-kv-extreme-scale"
+    ]
   }
 }