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

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

* 'findmnt-Q' of https://github.com/masatake/util-linux:
  tests: (findmnt) add a case testing -Q option
  findmnt: (man) write about -Q,--filter option
  findmnt: add -Q,--filter option
  findmnt: (refactor) convert add_column macro to a function
  findmnt: (refactor) add a helper function making an instance of libscols_table
  findmnt: (refactor) remove global variables shared between findmnt.c and fintmnt-verify.c