Packaging: Log stdout output into file

Until stdout was ignored during start up of our packages. This could
result in problems when specyfying something like an invalid heap size
(2gb instead of 2g) as this was not logged anywhere.

For init.d style startup, errors are now logged into
/var/log/elasticsearch/elasticsearch-stdout.log

For systemd startup, one can now use journalctl to see these errors.

This PR is based on #4429 (which only supported the debian package)