Fixes #4496: rudder-jetty package should conflict with standard jetty pa...

...ckages

See https://github.com/jooooooon/rudder-packages/compare/Normation:master...jooooooon:bug_4496%3Btrying_to_overwrite_etc_default_jetty_which_is_also_in_package_rudder_jetty_2_9_2_wheezy0?expand=1