provide Response Code and Message if Server Error on Write

[colinbjohnson]

Current Behavior:
When performing a write operation in which an error of >= 400 raises the ambiguous error 'Encountered server error'.

Desired Behavior:
The desired behavior would be to provide the actual response.code and, if available, response.message or similar.

Line/Modification Requested:
Currently in master, in file fluent-plugin-logdna/lib/fluent/plugin/out_logdna.rb, line 44 reads raise 'Encountered server error' if response.code >= 400. Link:

fluent-plugin-logdna/lib/fluent/plugin/out_logdna.rb

Line 44 in 6f28630

raise 'Encountered server error' if response.code >= 400