Doc Fix for 1267718

The following piece of documentaion is added to
account,container,object.cong-gluster file
"default gluster mount point to be used for
object store,can be changed by setting the following
value in {account,container,object}-server.conf files."

BUG:https://bugs.launchpad.net/gluster-swift/+bug/1267718

Change-Id: Icbdf7287153152e0173cef00b5336361081151c3
Signed-off-by: Pushpesh Sharma <psharma@redhat.com>
Reviewed-on: http://review.gluster.org/6692
Reviewed-by: Luis Pabon <lpabon@redhat.com>
Tested-by: Luis Pabon <lpabon@redhat.com>