issue-650 DynamicLoadBalancingPolicy: LatencyAwareHClientPool may throw NoSuchElementException under certain circumstances

Using the poll() method of the LinkedBlockingDeque prevent
NoSuchElementException throwing in case the deque is cleared by the
DynamicLoadBalancingPolicy resetThread.
Merge pull request #651 from jsbret/master

issue-650 DynamicLoadBalancingPolicy: LatencyAwareHClientPool may throw ...