LU-8599 utils: restore lshowmount utility

The lshowmount utility was removed in commit b5a7260ae8f as being
obsolete, but it was not as unused as previously thought.

Restore lshowmount.c, lshowmount.8, nidlist.c, and nidlist.h  from
history, with minor updates to the Makefiles and .gitignore to avoid
conflicts in context.

Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Yang Sheng <yang.sheng@intel.com>
Change-Id: Ibf6f72684d4dcaa95e0366b4fde74386893ebbe5
Reviewed-on: http://review.whamcloud.com/17593
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Thomas Stibor <t.stibor@gsi.de>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>