Description
Related to HBASE-16138. As of now we currently have no pause between retrying failed region open requests. And with a low maximumAttempt default, we can quickly use up all our regionOpen retries if the server is in a bad state. I added in a ExponentialBackOffPolicy so that we spread out the timing of our open region retries in AssignmentManager. Review board at https://reviews.apache.org/r/50011/