TestNameNodeMetrics fails on Windows

TestNameNodeMetrics fails on Windows

Problem:

This is because in testVolumeFailures, it tries to call DataNodeTestUtils.injectDataDirFailure on a volume folder. What injectDataDirFailure does is actually modifying the folder name from volume_name to volume_name.origin and create a new file named as volume_name. Inside the folder, it has two things: 1. a directory named as "current", 2. a file named as "in_use.lock". Windows behaves different from Linux when renaming the parent folder of a locked file. Windows prevent you from renaming while Linux allows.

Fix:

So in order to inject data failure on to the volume. Instead of renaming the volume folder itself. Rename the folder inside it which doesn't hold a lock. Since the folder inside the volume is "current". Then we only need to inject data failure to volume_name/current.