Create Jetty Base directories in the Permanent Directory

Since the upgrade to Jetty 9.2.13.v20150730, Jetty now creates empty directories for logs, lib, webapps, etc in its Jetty Base directory (This is the location for your configurations and customizations to the Jetty distribution. See http://www.eclipse.org/jetty/documentation/current/startup-base-and-home.html for more).

In order to prevent cryptic warning messages displayed in the console when Jetty starts the first time, we added creation of those directories in XWIKI-12682. However we didn't modify the Jetty Base directory which is pointing to the Jetty Home directory (where default Jetty config is located).

As a consequence this change is causing some problems:

• On Windows the Jetty Home directory is read only and thus we cannot have the Jetty Base in there.
• It's not a good idea to modify an installation directory at runtime. Thus it's better to move the Jetty Base directory to our Permanent Directory, thus keeping the user's customization of Jetty across XWiki upgrades for example.