[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>
Thanks for the explanation. So according to my understanding, to run the integration test, the user needs to prepare their glusterfs by configuring corresponding items (e.g., mount point based on the real deployment). And the ufs test folder is always under tachyon_test folder. This one is not configurable. Right?