Made rqworker and rqinfo respect db parameters from --url

When starting the rqworker and rqinfo scripts with an --url parameter containing a non default database, e.g. redis://localhost:6379/2, both scripts connected db 0 instead of the desired database. Fixed this behavior by ignoring the --host, --port and --db arguments if --url is there.

Also fixed another issue with the rqinfo script, in which it defaulted to only the 'default' queue instead of finding all available queues using Queue.all().
Merge pull request #198 from johannth/scripts-respect-url

Made rqworker and rqinfo respect db parameters from --url