Change severity of logs for certain gRPC status codes

[limemloh]

Purpose

Fixes #1057

Changes

• Using DEBUG severity for logging of failed gRPC API requests.

Checklist

• My code follows the style of this project.
• The code compiles without warnings.
• I have performed a self-review of the changes.
• I have documented my code, in particular the intent of the
  hard-to-understand areas.
• (If necessary) I have updated the CHANGELOG.

[lassemand]

Looks good to me.

I believe it would make more sense to also include RESOURCE_EXHAUSTED but I can also argue for why it should not be there. I do believe this one is usually cast when the node is gracefully exhausted. (Else it would be down?)

If a person tries to DoS us what should we do? On the one hand it would be nice to provide the error logs, but on the other hand, the server is not in a bad state, only the client is unable to request the server.

I can accept both.

[td202]

Looks good!