LU-12159 utils: improve lfs getname functionality

LU-12159 utils: improve lfs getname functionality

Add "-n" and "-i" options to lfs getname to allow printing only
the fsname or instance ID of the filesystem(s).

Split out the documentation to a separate lfs-getname.1 man page.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Ie132513325b6630fc5103a89b469271ba7392cb2
Reviewed-on: https://review.whamcloud.com/34595
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Ben Evans <bevans@cray.com>
Reviewed-by: Arshad Hussain <arshad.super@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>