Add helper function so that IAM policies can be compared for equality and update s3_bucket to take advantage of helper function

lib/ansible/modules/cloud/amazon/GUIDELINES.md

@@ -233,6 +233,34 @@ result = connection.aws_call()
 module.exit_json(changed=True, **camel_dict_to_snake_dict(result))
 ```
 
+### Dealing with IAM JSON policy
+
+If your module accepts IAM JSON policies then set the type to 'json' in the module spec. For example"
+
+```python
+argument_spec.update(
+    dict(
+        policy=dict(required=False, default=None, type='json'),
+    )
+)
+```
+
+Note that AWS is unlikely to return the policy in the same order that is was submitted. Therefore, a helper
+function has been created to order policies before comparison.
+
+```python
+# Get the policy from AWS
+current_policy = aws_object.get_policy()
+
+# Compare the user submitted policy to the current policy but sort them first
+if sort_json_policy_dict(user_policy) == sort_json_policy_dict(current_policy):
+    # Nothing to do
+    pass
+else:
+    # Update the policy
+    aws_object.set_policy(user_policy)
+```
+
 ### Helper functions
 
 Along with the connection functions in Ansible ec2.py module_utils, there are some other useful functions detailed below.
@@ -261,4 +289,10 @@ Opposite of above. Converts an Ansible dict to a boto3 tag list of dicts.
 
 Pass this function a list of security group names or combination of security group names and IDs and this function will
 return a list of IDs.  You should also pass the VPC ID if known because security group names are not necessarily unique
-across VPCs.
+across VPCs.
+
+### sort_json_policy_dict
+
+Pass any JSON policy dict to this function in order to sort any list contained therein. This is useful
+because AWS rarely return lists in the same order that they were submitted so without this function, comparison
+of identical policies returns false.

lib/ansible/modules/cloud/amazon/s3_bucket.py

@@ -213,7 +213,7 @@ def _create_or_update_bucket(connection, module, location):
             # only show changed if there was already a policy
             changed = bool(current_policy)
 
-        elif current_policy != policy:
+        elif sort_json_policy_dict(current_policy) != sort_json_policy_dict(policy):
             try:
                 bucket.set_policy(json.dumps(policy))
                 changed = True