XWIKI-10826: Impossible to run 2 instances of XWiki on same Tomcat instance because of Solr
- Using only xwiki.properties to configure Solr's home directory, ignoring any system property or any environment/JNDI entry.
- Fixed tests

(cherry picked from commit a169e9092a68e83c7ac1545cd4e0d01a36bb8a75)