Update Xwiki using a proxy

[tmortagne]

@jingkaimori

I’m using tomcat with catalina installed by deb package, so the settings locate in /usr/share/tomcat9/bin/catalina.sh

Actually as suggested on https://www.xwiki.org/xwiki/bin/view/Documentation/AdminGuide/Installation/InstallationViaAPT/#HTomcat-1 a more accurate configuration file is /etc/default/tomcat9.