do not add group as role

git-svn-id: https://svn.apache.org/repos/asf/archiva/redback/redback-core/trunk@1437034 13f79535-47bb-0310-9956-ffa450edef68
if using useDefaultRoleName we must check role really exists

git-svn-id: https://svn.apache.org/repos/asf/archiva/redback/redback-core/trunk@1437035 13f79535-47bb-0310-9956-ffa450edef68