Fixed outdated ECR credential debug message (#18631)

* Fixed outdated ECR credential debug message

The log message for troubleshooting kubelet auto fetching ECR credentils issue has been changed (noticed since 1.14), and the new message reads like this when verbose log level is set to 3:

      - `aws_credentials.go:109] unable to get ECR credentials from cache, checking ECR API`
      - `aws_credentials.go:116] Got ECR credentials from ECR API for <Your ECR AWS Account ID>.dkr.ecr.us-east-1.amazonaws.com`

This is based on the kubelet source code: 
    https://github.com/kubernetes/kubernetes/blob/release-1.14/pkg/credentialprovider/aws/aws_credentials.go#L91

This PR is to fix this and to avoid confusion for more people who are troubleshooting the kubelet ECR issue.

* Update content/en/docs/concepts/containers/images.md

Co-Authored-By: Tim Bannister <tim@scalefactory.com>

Co-authored-by: Tim Bannister <tim@scalefactory.com>

content/en/docs/concepts/containers/images.md

@@ -124,9 +124,9 @@ Troubleshooting:
 - Verify all requirements above.
 - Get $REGION (e.g. `us-west-2`) credentials on your workstation. SSH into the host and run Docker manually with those creds. Does it work?
 - Verify kubelet is running with `--cloud-provider=aws`.
-- Check kubelet logs (e.g. `journalctl -u kubelet`) for log lines like:
-  - `plugins.go:56] Registering credential provider: aws-ecr-key`
-  - `provider.go:91] Refreshing cache for provider: *aws_credentials.ecrProvider`
+- Increase kubelet log level verbosity to at least 3 and check kubelet logs (e.g. `journalctl -u kubelet`) for log lines like:
+  - `aws_credentials.go:109] unable to get ECR credentials from cache, checking ECR API`
+  - `aws_credentials.go:116] Got ECR credentials from ECR API for <AWS account ID for ECR>.dkr.ecr.<AWS region>.amazonaws.com`
 
 ### Using Azure Container Registry (ACR)
 When using [Azure Container Registry](https://azure.microsoft.com/en-us/services/container-registry/)