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
I'm pretty sure we don't want to install an empty file.

My understanding of the %ghost directive is that you can just specify it, and RPM will "own" the file, but not install it. Since you don't install it, you don't need it.

Did you test this with just the "%ghost", and no file, and have problems? If so, please explain what they were.