Add getEnclosingRoot() API to filesystem interface and implementations

At LinkedIn we run many HDFS volumes that are federated by either ViewFilesystem or Router Based Federation. As our number of hdfs volumes grows, we have a growing need to migrate data seemlessly across volumes.

Many frameworks have a notion of staging or temp directories, but those directories often live in random locations. We want an API getEnclosingRoot, which provides the root path a file or dataset. 

In ViewFilesystem / Router Based Federation, the enclosingRoot will be the mount point.

We will also take into account other restrictions for renames like encryptions zones.

If there are several paths (a mount point and an encryption zone), we will return the longer path