Actually, deleting these lines won't impact the unit-test now. since I only disabled the instance cache for that  MasterFaultToleranceTest. 

Say in the real-world deployment, it might have some potential issue here. If one master hangs, and the standby node start-up to create the first editlog. There happens the situation of creating the same file by different clients. And some AlreadyBeingCreatedException will be thrown in the creation line. 

However it seems that the problem has been solved by HDFS-3755 (since hadoop 3.0.0, 2.0.2-alpha). I have tested with hadoop.version=2.2.0. It does work even without deletion before hand. 

Since we need to support those previous versions as well. I think it is better to do so here.  

BTW, sorry again for that code convention issue. I will fix it immediately.