Update Cockpit 'main screen' needle

It seems like sometimes the machine ID is off the bottom of the
screen now, so let's just match on the section title instead.

Signed-off-by: Adam Williamson <awilliam@redhat.com>

needles/cockpit/cockpit_main-20200505.json

@@ -0,0 +1,15 @@
+{
+  "area": [
+    {
+      "type": "match",
+      "height": 27,
+      "ypos": 671,
+      "width": 213,
+      "xpos": 238
+    }
+  ],
+  "properties": [],
+  "tags": [
+    "cockpit_main"
+  ]
+}