Use httputil DumpRequest instead of just %v formatting

This makes logplexd output a lot more useful in most cases.
DumpRequest is set up to render the request body, also.

Signed-off-by: Daniel Farina <daniel@fdr.io>
Log dropping has since been implemented in logplexc.

Timeouts will probably end up being similar, leaving less in
pg_logplexcollector.

Signed-off-by: Daniel Farina <daniel@fdr.io>