Fix for writing config attribute 'max_retries' for aws auth method

[andrejvanderzee]

After a client config is created for the AWS auth method, we can't change max_retries without first deleting the client config. Because, for existing configs max_retries the config is not pushed to backend storage:

$ vault write auth/team7/aws/k8s/node/config/client max_retries=20
Success! Data written to: auth/team7/aws/k8s/node/config/client
$ vault read auth/team7/aws/k8s/node/config/client
Key                           Value
---                           -----
access_key                    n/a
endpoint                      n/a
iam_endpoint                  n/a
iam_server_id_header_value    n/a
max_retries                   10
sts_endpoint                  n/a

Please merge this fix so we can delete our workaround.

[jefferai]

Thanks!

[andrejvanderzee]

That was a quick merge, thanks!