Update Curator to 2.4.0 when its available to fix security hole

As I discovered when working on OOZIE-1491, there is a Curator bug (CURATOR-58) without which the ZooKeeper locks will always have world ACLs even with Kerberos enabled. This could allow a malicious user to acquire one of the locks and never release it, thus preventing Oozie from continuing to process the job associated with that lock.

I've verified that CURATOR-58 fixes the problem, and the locks have the correct "sasl" ACLs, but it won't be available until Curator 2.4.0 is released. We should make sure to update to Curator 2.4.0 as soon as possible to fix this security hole.