kt: Retry on all errors, not just io.EOF
kt: Retry on all errors, not just io.EOF

There are several errors in addition to io.EOF which net/http will return when connections in the pool are cut:

* http.errServerClosedIdle: returned if the request is not idempotent, possibly a race in net/http
* net.Errors: returned if request is written to connection closed by remote end

http.errServerClosedIdle is especially troublesome, since it isn't exported by net/http. Instead of kludging a check for the unexported error we simply retry on all errors.

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