experimental xlators not included in 3.12

Cherry picked from 4231c40973c60999f5ef759db450d25e129ef6ba:
> Change-Id: I547480ee5e7912664784643e436feb198b6d16d0
> BUG: 1447543
> Signed-off-by: Kaushal M <kaushal@redhat.com>
> Reviewed-on: https://review.gluster.org/17154
> Smoke: Gluster Build System <jenkins@build.gluster.org>
> NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
> Reviewed-by: Amar Tumballi <amarts@redhat.com>
> CentOS-regression: Gluster Build System <jenkins@build.gluster.org>

Change-Id: I34419ce22ca09b7626b8f9382c377a614fd9fed8
BUG: 1477381
Signed-off-by: ShyamsundarR <srangana@redhat.com>
Reviewed-on: https://review.gluster.org/17953
Smoke: Gluster Build System <jenkins@build.gluster.org>
Reviewed-by: jiffin tony Thottan <jthottan@redhat.com>
CentOS-regression: Gluster Build System <jenkins@build.gluster.org>

DHT2 comes with a new backend on-disk format, that requires
a new backend storage xlator. This experimental project will
house the artifacts for the same.

Change-Id: I71a3d60a0415d0c23b2294a02b838810fa8f101f
BUG: 1338991
Signed-off-by: Shyam <srangana@redhat.com>
Reviewed-on: http://review.gluster.org/14646
Smoke: Gluster Build System <jenkins@build.gluster.com>
NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
CentOS-regression: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>