[Tachyon-26] test UnderFileSystem.get() code path in Glusterfs Cluster.

Fix the dependency issue in gluster test profile;
Update gluster test instruction in glusterfs setup document.

Signed-off-by: rootfs <hchen@redhat.com>
I don't think it is a bug. The test environment(for hdfs or localfs) is brand new before. But the glusterfs re-uses the test environment. That's why it needs to cleanup the folder, otherwise it will see some creation exception. Right? @rootfs