LU-8055 ldev: Add %H and %b to command sub

LU-8055 ldev: Add %H and %b to command sub

Introduced %H and %b substitutions for hostname
and backend file system, respectively.

Test-Parameters: trivial testlist=conf-sanity
Signed-off-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Change-Id: I9b50defee43307f614106de4ad75e1fa9267e23b
Reviewed-on: http://review.whamcloud.com/20040
Reviewed-by: Olaf Faaland-LLNL <faaland1@llnl.gov>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Christopher J. Morrone <morrone2@llnl.gov>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>