LU-9946 nodemap: have fileset on default nodemap.

LU-9946 nodemap: have fileset on default nodemap.

When a directory is defined as fileset on the default nodemap entry,
all clients that fall into default will be imposed subdirectory
mount on this directory.

Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I3491bce4f8c2011629e56494bf1a0de57f19829d
Reviewed-on: https://review.whamcloud.com/28858
Tested-by: Jenkins
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Emoly Liu <emoly.liu@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>