ACCUMULO-727 add exponential back-off when bulk loading files

git-svn-id: https://svn.apache.org/repos/asf/accumulo/branches/1.5@1457055 13f79535-47bb-0310-9956-ffa450edef68
ACCUMULO-727 add exponential back-off when bulk loading files

git-svn-id: https://svn.apache.org/repos/asf/accumulo/trunk@1457056 13f79535-47bb-0310-9956-ffa450edef68