fs-lib: drop a bashism
    
    Bash 5 apparently longer propagates variable assignments to local variables
    in front of function calls when in POSIX mode:
    
      [lkundrak@demiurge ~]$ cat feh.sh
      print_VAR () {
              echo "$VAR";
      }
    
      testfunc () {
              local VAR="OLD"
              VAR=NEW print_VAR
      }
    
      testfunc
      [lkundrak@demiurge ~]$ bash4 --posix feh.sh
      NEW
      [lkundrak@demiurge ~]$ bash5 --posix feh.sh
      OLD
      [lkundrak@demiurge ~]$ bash5 feh.sh
      NEW
      [lkundrak@demiurge ~]$
    
    It works the way it did in Bash 4 in non-POSIX mode, for external programs,
    or for non-local variables. Don't ask me why -- it's probably some
    compatibility thing for some sad old people.
    
    However, this precisely happens when fsck_single() is calling into the
    fsck_drv_com(), assigned to _drv by fsck_able(). That ruins the
    TEST-70-BONDBRIDGETEAMVLAN test's server and probably more.
    
    Let's pass the fsck driver binary via the function argument instead. It's
    less messy anyway.
    
    (cherry picked from commit 43c8c4ce0471abbb8c0fc4b8be2515cebc636030)
    
    patch_name: 0028.patch
    present_in_specfile: true
    location_in_specfile: 28
    squash_commits: true