SH-3331 Fix incorrect overrun message when sending body with HTTP

request.  During readcallback, would generate an overrun-type message
about reading position beyond end-of-data.  Mistake was is messaging
when state is exactly at end of data (which is expected) versus an
overrun.  Both result in declaring end-of-data to libcurl.  Also
changed some of the status logging for the metrics payload to be
less chatty on success, more informative on error.