LU-14262 utils: lfs to set component flags by pool name

LU-14262 utils: lfs to set component flags by pool name

so it'd be easy to set flags (like prefer) on the components
residing on specific OST identified by pool.

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: I733f92fe186682dc8d34512edf75b49e565c457f
Reviewed-on: https://review.whamcloud.com/41024
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>