STANBOL-811: Corrected an issue (introduced with the last commit) where the SolrCore folder where created/deleted for each call to performCVFold(..) instead of once per call to updatePerformanceEstimates(..). The new version is more similar to the original one.

git-svn-id: https://svn.apache.org/repos/asf/stanbol/trunk@1450758 13f79535-47bb-0310-9956-ffa450edef68