Unify the retry logic in ScannerCallableWithReplicas and RpcRetryingCallerWithReadReplicas

The issue is pointed out by devaraj in HBASE-16132 (Thanks D.D.), that in RpcRetryingCallerWithReadReplicas#call we will call ResultBoundedCompletionService#take instead of poll to dead-wait on the second one if the first replica timed out, while in ScannerCallableWithReplicas#call we still use ResultBoundedCompletionService#poll with some timeout for the 2nd replica.

This JIRA aims at discussing whether to unify the logic in these two kinds of caller with region replica and taking action if necessary.