extra: "enable-shared-storage" key should create shared-storage

extra: "enable-shared-storage" key should create shared-storage

Currently while creating shared storage it accept only
"cluster.enable-shared-storage" key. It should also
accept "enable-shared-storage" key.

Change-Id: I4c68782f4b7927ec8cd725e411b0b9db17d9c48d
BUG: 1238224
Signed-off-by: Gaurav Kumar Garg <ggarg@redhat.com>
Reviewed-on: http://review.gluster.org/11491
Tested-by: NetBSD Build System <jenkins@build.gluster.org>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Krishnan Parthasarathi <kparthas@redhat.com>
Reviewed-by: Avra Sengupta <asengupt@redhat.com>