[MSITE-713] removed "Error during page generation" error message, improved "Error rendering Maven report" by adding precise report information

git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/trunk@1598319 13f79535-47bb-0310-9956-ffa450edef68
reorganized code and added comments to better understand the intent

git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/trunk@1598320 13f79535-47bb-0310-9956-ffa450edef68