Enforce all dicts with a fixed set of keys in test.json schema

Improve test.json schema to disallow arbitrary keys in all dicts which
have a defined set of keys (the 'installed', matrix 'options' and
'stdout' dicts).

Add 'count' and 'comment' keys to 'stdout' dict.

data/test.schema.json

@@ -12,6 +12,7 @@
       "type": "array",
       "items": {
         "type": "object",
+        "additionalProperties": false,
         "properties": {
           "file": {
             "type": "string"
@@ -59,6 +60,7 @@
             "type": "array",
             "items": {
               "type": "object",
+              "additionalProperties": false,
               "properties": {
                 "val": {
                   "type": "string"
@@ -110,6 +112,7 @@
       "type": "array",
       "items": {
         "type": "object",
+        "additionalProperties": false,
         "properties": {
           "line": {
             "type": "string"
@@ -120,6 +123,12 @@
               "literal",
               "re"
             ]
+          },
+          "count": {
+            "type": "integer"
+          },
+          "comment": {
+            "type": "string"
           }
         },
         "required": [