This is to verify:
- Evict RAM_DISK block with open handle should fall back to DISK.
- Delete RAM_DISK block (persisted) with open handle should mark the block to be deleted upon handle close.
Simply open handle to file in DFS name space won't work as expected. We need a local FS file handle to the block file. The only meaningful case is for Short Circuit Read. This JIRA is to validate/enable the two cases with SCR enabled MiniDFSCluster.