Fix init script in Ubuntu/Debian and Redhat/Centos

Fix issue with wrong pidfile being created by start-stop-daemon.

Using -b on webrick makes it fork right after starting, leaving the pidfile created by start-stop-daemon pointing to a non-existing process. Removed -b so webrick woudn't fork.

On Ubuntu, using start-stop-daemon's --background switch instead.
On Redhat, relying on daemon's default behavior.