Merge branch 'lsns--Q' of https://github.com/masatake/util-linux

Merge branch 'lsns--Q' of https://github.com/masatake/util-linux

* 'lsns--Q' of https://github.com/masatake/util-linux:
  tests: (lsns) add a case testing -Q, --filter option
  tests: (test_mkfds::userns) add a new factory
  tests: (test_mkfds::multiplexing) fix the factory description
  lsns: add -H, --list-columns option
  lsns: implement -Q, --filter option
  lsfd: (man) fix the decoration of an optional parameter
  lsns: add a missing '=' character in the help message
  lsns: (man) make the namespace parameter optional
  lsblk: (refactor) refer to a parameter instead of a file static var