LU-8055 ldev: File system label filtering

Introduced -F option to ldev. The -F requires
a file system name to be provided. All labels
associated with that file system will be
printed to stdout. The new option can also be
used with command substitution.

Test-Parameters: trivial testlist=conf-sanity

Signed-off-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Change-Id: I50726371dce809e4d1b4f3de6f530d6f637856a1
Reviewed-on: http://review.whamcloud.com/19738
Tested-by: Jenkins
Reviewed-by: Olaf Faaland-LLNL <faaland1@llnl.gov>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Christopher J. Morrone <morrone2@llnl.gov>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>