SLING-3382 : introducing connector frequency backoff behavior: when a connector sends stable announcement, the servlet instructs the client to backoff, ie send with a higher heartbeatInterval, up to a configurable maximum, default is 5 times the heartbeatInterval

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1569389 13f79535-47bb-0310-9956-ffa450edef68