Fixes #5223 - Fix migration of rudder-webapp to 2.11 on RPM

Fixes #5223 - Fix migration of rudder-webapp to 2.11 on RPM

cf http://www.rudder-project.org/redmine/issues/5223

The migration removed the file /opt/rudder/jetty7/contexts/rudder.xml since it was not owned by package.

I've built a package to try the patch and it worked