gNFS : make it possible to mount a subdir that actually is a symlink

We are using the function to export all sub-directories in a gluster volume via nfs.
For real directories it works fine but if we have a symbolic link which points to the
directory, it is not possible to mount that directory via nfs and the nameof the link.
Kernel nfs resolves symlink handle to directoryhandle , similar gluster nfs should
resolve the symbolic link handle into directory handle.

Change-Id: I8bd07534ba9474f0b863f2335b2fd222ab625dba
BUG: 1157223
Signed-off-by: jiffin tony thottan <jthottan@redhat.com>
Reviewed-on: http://review.gluster.org/9052
Reviewed-by: soumya k <skoduri@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>
Reviewed-by: Niels de Vos <ndevos@redhat.com>