Yaml inventory more tolerant (#48883)

* make yaml inv more tolerant to comments
* add tests for bad inventory processing

fixes #47254

test/integration/targets/inventory_yaml/aliases

@@ -0,0 +1 @@
+shippable/posix/group1

test/integration/targets/inventory_yaml/empty.json

@@ -0,0 +1,10 @@
+{
+    "_meta": {
+        "hostvars": {}
+    }, 
+    "all": {
+        "children": [
+            "ungrouped"
+        ]
+    }
+}

test/integration/targets/inventory_yaml/runme.sh

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+
+# handle empty/commented out group keys correctly https://github.com/ansible/ansible/issues/47254
+ANSIBLE_VERBOSITY=0 diff -w <(ansible-inventory -i ./test.yml --list) success.json

test/integration/targets/inventory_yaml/success.json

@@ -0,0 +1,61 @@
+{
+    "_meta": {
+        "hostvars": {
+            "alice": {
+                "status": "single"
+            }, 
+            "bobby": {
+                "in_trouble": true, 
+                "popular": false
+            }, 
+            "cindy": {
+                "in_trouble": true, 
+                "popular": true
+            }, 
+            "greg": {
+                "in_trouble": true, 
+                "popular": true
+            }, 
+            "jan": {
+                "in_trouble": true, 
+                "popular": false
+            }, 
+            "marcia": {
+                "in_trouble": true, 
+                "popular": true
+            }, 
+            "peter": {
+                "in_trouble": true, 
+                "popular": false
+            }
+        }
+    }, 
+    "all": {
+        "children": [
+            "cousins", 
+            "kids", 
+            "the-maid", 
+            "ungrouped"
+        ]
+    }, 
+    "cousins": {
+        "children": [
+            "redheads"
+        ]
+    }, 
+    "kids": {
+        "hosts": [
+            "bobby", 
+            "cindy", 
+            "greg", 
+            "jan", 
+            "marcia", 
+            "peter"
+        ]
+    }, 
+    "the-maid": {
+        "hosts": [
+            "alice"
+        ]
+    }
+}

test/integration/targets/inventory_yaml/test.yml

@@ -0,0 +1,27 @@
+all:
+    children:
+        kids:
+            hosts:
+                marcia:
+                    popular: True
+                jan:
+                    popular: False
+                cindy:
+                    popular: True
+                greg:
+                    popular: True
+                peter:
+                    popular: False
+                bobby:
+                    popular: False
+            vars:
+                in_trouble: True
+        cousins:
+            children:
+                redheads:
+                    hosts:
+                        #oliver:  # this used to cause an error and deliver incomplete inventory
+        the-maid:
+            hosts:
+                alice:
+                    status: single