Enable jetty's request log by default

I'd like to enable the jetty request log by default.

This log is now in the correct directory, it no longer uses the deprecated mechanisms (it is asynclogwriter + customformat), etc. See SOLR-14138.

This log is in a standard format (NCSA) which is supported by tools out-of-box. It does not contain challenges such as java exceptions and is easy to work with. Without it enabled, solr really has insufficient logging (e.g. no IP addresses).

If someone's solr gets hacked, its only fair they at least get to see who did it.