LU-17516 utils: new --mdt and --ost options for lfs df

LU-17516 utils: new --mdt and --ost options for lfs df

Added [--mdt | -m] and [--ost | -o] options for 'lfs df' to print
only usage of the respective MDT or OST devices in mntdf(). If both
"--mdt" and "--ost" are specified it will show both types of devices
which is identical to having neither specified.

Signed-off-by: Frederick Diger <fdilger@whamcloud.com>
Change-Id: I196b7c9c0c385850372331587936fa5cf6b71d93
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/55156
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Timothy Day <timday@amazon.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>