Also send system information when saving Active Install pings

The idea is to send the following pieces of information too:

• Java vendor and version
• OS name, arch and version
• Database product name and version
• Servlet container name and version

This will allow us to know more our use base and evaluate better the consequences of moving from one version of Java to another, what are the most used DBs on XWiki, what OS is the most used for XWiki, etc. This is useful to understand where to focus our support efforts for example.

See also http://design.xwiki.org/xwiki/bin/view/Proposal/ActiveInstalls2