LU-2430 utils: fix "lfs mv" command parsing

LU-2430 utils: fix "lfs mv" command parsing

Fix the lfs_mv() long option parsing so that it uses "--mdt-index"
instead of incorrectly requiring "----mdt-index" for the short "-M"
option.

Fix up some error messages in lfs_mv() as well, and change a test
case to use the long option form.

Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: I20ffde97fb5d31364e91d6b21d407eb3323ebbe5
Reviewed-on: http://review.whamcloud.com/13161
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Reviewed-by: wangdi <di.wang@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>