molecule: recognize platform children

f/molecule.json

@@ -106,6 +106,12 @@
           "title": "Box",
           "type": "string"
         },
+        "children": {
+          "items": {
+            "type": "string"
+          },
+          "type": "array"
+        },
         "command": {
           "title": "Command",
           "type": "string"

negative_test/molecule/platforms_children/molecule.yml

@@ -0,0 +1,5 @@
+driver:
+  name: delegated
+platforms:
+  - name: foo
+    children: 2 # invalid, must be list of strings

test/molecule/default/molecule.yml

@@ -31,6 +31,7 @@ log: true
 platforms:
   - name: ubi8
     hostname: ubi8
+    children: [] # list of strings
     unknown_property_foo: bar # unknown properties should be allowed for drivers
     groups:
       - ubi8
@@ -57,6 +58,7 @@ platforms:
 
   - name: ubi7
     hostname: ubi7
+    children: ["ubi8"]
     groups:
       - ubi7
     image: ubi7/ubi-init