drill

0a4c21cc - DRILL-4836: Handle NodeExistsException in ZookeeperClient#put (race condition)

DRILL-4836: Handle NodeExistsException in ZookeeperClient#put (race condition) ZK Issue during Drillbit startup, possibly due to race condition. A change made in February created a race condition if two Drillbits attempt to create the same storage plugin node at the same time. Revised the code to eliminate the race condition by relying on an exception to detect that the node already exists. closes #564