ACCUMULO-1334 add disk usage to the API

git-svn-id: https://svn.apache.org/repos/asf/accumulo/branches/1.5@1478068 13f79535-47bb-0310-9956-ffa450edef68
ACCUMULO-1334 add disk usage to the API

git-svn-id: https://svn.apache.org/repos/asf/accumulo/branches/1.5@1478069 13f79535-47bb-0310-9956-ffa450edef68