[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>
yes, we have to provide the mount point. The uri glusterfs:///tachyon_test means the directory under the mount point.