Seeing interrupted exception when closing PathChildrenCache

After patch for #206 seeing alot of the following exceptions. Looking into this, @cjnolet may have had the issue fixed in [CURATOR-121](https://issues.apache.org/jira/browse/CURATOR-121). Going to curator 2.7 may make these exceptions go away.

```
2015-02-07 11:20:44,152 [server.AbstractNonblockingServer$FrameBuffer] ERROR: Unexpected throwable while invoking!
java.lang.IllegalStateException
at io.fluo.core.oracle.OracleServer._getTimestamps(OracleServer.java:158)
at io.fluo.core.oracle.OracleServer.getTimestamps(OracleServer.java:141)
at io.fluo.core.thrift.OracleService$Processor$getTimestamps.getResult(OracleService.java:224)
at io.fluo.core.thrift.OracleService$Processor$getTimestamps.getResult(OracleService.java:209)
at org.apache.thrift.ProcessFunction.process(ProcessFunction.java:39)
at org.apache.thrift.TBaseProcessor.process(TBaseProcessor.java:39)
at org.apache.thrift.server.AbstractNonblockingServer$FrameBuffer.invoke(AbstractNonblockingServer.java:516)
at org.apache.thrift.server.Invocation.run(Invocation.java:18)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745)
2015-02-07 11:20:45,887 [cache.PathChildrenCache] ERROR:
org.apache.zookeeper.KeeperException$NoNodeException: KeeperErrorCode = NoNode for /oracle/server/_c_31687f18-40ca-4ec2-881d-7a08a67028c8-lock-0000000000
at org.apache.zookeeper.KeeperException.create(KeeperException.java:111)
at org.apache.zookeeper.KeeperException.create(KeeperException.java:51)
at org.apache.zookeeper.ZooKeeper.getData(ZooKeeper.java:1155)
at org.apache.curator.framework.imps.GetDataBuilderImpl$4.call(GetDataBuilderImpl.java:302)
at org.apache.curator.framework.imps.GetDataBuilderImpl$4.call(GetDataBuilderImpl.java:291)
at org.apache.curator.RetryLoop.callWithRetry(RetryLoop.java:107)
at org.apache.curator.framework.imps.GetDataBuilderImpl.pathInForeground(GetDataBuilderImpl.java:287)
at org.apache.curator.framework.imps.GetDataBuilderImpl.forPath(GetDataBuilderImpl.java:279)
at org.apache.curator.framework.imps.GetDataBuilderImpl.forPath(GetDataBuilderImpl.java:41)
at org.apache.curator.framework.recipes.leader.LeaderSelector.participantForPath(LeaderSelector.java:374)
at org.apache.curator.framework.recipes.leader.LeaderSelector.getLeader(LeaderSelector.java:345)
at org.apache.curator.framework.recipes.leader.LeaderSelector.getLeader(LeaderSelector.java:338)
at io.fluo.core.oracle.OracleServer.childEvent(OracleServer.java:330)
at org.apache.curator.framework.recipes.cache.PathChildrenCache$5.apply(PathChildrenCache.java:509)
at org.apache.curator.framework.recipes.cache.PathChildrenCache$5.apply(PathChildrenCache.java:503)
at org.apache.curator.framework.listen.ListenerContainer$1.run(ListenerContainer.java:92)
at com.google.common.util.concurrent.MoreExecutors$SameThreadExecutorService.execute(MoreExecutors.java:262)
at org.apache.curator.framework.listen.ListenerContainer.forEach(ListenerContainer.java:83)
at org.apache.curator.framework.recipes.cache.PathChildrenCache.callListeners(PathChildrenCache.java:500)
at org.apache.curator.framework.recipes.cache.EventOperation.invoke(EventOperation.java:35)
at org.apache.curator.framework.recipes.cache.PathChildrenCache$10.run(PathChildrenCache.java:762)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
at java.util.concurrent.FutureTask.run(FutureTask.java:262)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
at java.util.concurrent.FutureTask.run(FutureTask.java:262)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745)

```