logging of http request may empty input data

[dataclouder]

The logging of HTTP requests in api.go may empty the data when the body is not a *bytes.Buffer.

Most of the requests in the API are created using a *bytes.Buffer, but some aren't. When the body is some other kind of io.Reader, copying the contents will empty the buffer, and the request will fail.

To fix it, we will check whether the body type is *bytes.Buffer and make the copy only in that case.