LU-16232 scripts: clean specific MDTs update llogs

LU-16232 scripts: clean specific MDTs update llogs

Modify remove_updatelog script as following:
- avoid bash-specific process substitution for compatibility
- add '-m <index,...> option to select only specific MDTs to
  process through their update llogs only
- add test to check script actions

Signed-off-by: Mikhail Pershin <mpershin@whamcloud.com>
Change-Id: Icd935d5f4964d364f38b4962355ef8a5e679dbb3
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/50558
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Colin Faber <cfaber@ddn.com>