Cleanup - use is_boto3_error_(message|code) (ansible-collections#268)

* Reorder imports
* Make use of is_boto3_error_message
* Mass-migration over to is_boto3_error_code
* Remove unused imports
* unused vars in exception
* Improve consistency around catching BotoCoreError and ClientError
* Remove unused imports
* Remove unused 'PolicyError' from iam_policy_info
* Avoid catching botocore.exceptions.ClientError when we only want some error codes
* Import camel_dict_to_snake_dict/snake_dict_to_camel_dict from ansible.module_utils.common.dict_transformations

This commit was initially merged in https://github.com/ansible-collections/community.aws
See: ansible-collections@4cf52ef

plugins/modules/iam_policy_info.py

@@ -78,18 +78,15 @@
 '''
 
 try:
-    from botocore.exceptions import BotoCoreError, ClientError
+    import botocore
 except ImportError:
     pass
 
 from ansible_collections.amazon.aws.plugins.module_utils.core import AnsibleAWSModule
+from ansible_collections.amazon.aws.plugins.module_utils.core import is_boto3_error_code
 from ansible_collections.amazon.aws.plugins.module_utils.ec2 import AWSRetry
 
 
-class PolicyError(Exception):
-    pass
-
-
 class Policy:
 
     def __init__(self, client, name, policy_name):
@@ -202,12 +199,10 @@ def main():
             policy = GroupPolicy(**args)
 
         module.exit_json(**(policy.run()))
-    except (BotoCoreError, ClientError) as e:
-        if e.response['Error']['Code'] == 'NoSuchEntity':
-            module.exit_json(changed=False, msg=e.response['Error']['Message'])
+    except is_boto3_error_code('NoSuchEntity') as e:
+        module.exit_json(changed=False, msg=e.response['Error']['Message'])
+    except (botocore.exceptions.ClientError, botocore.exceptions.BotoCoreError) as e:  # pylint: disable=duplicate-except
         module.fail_json_aws(e)
-    except PolicyError as e:
-        module.fail_json(msg=str(e))
 
 
 if __name__ == '__main__':