fstests: fix build issues

Dave Chinner
2021-10-10T23:25:24Z

Hi folks,

With Debian unstable moving all it's userspace forwards after the
recent release, fstests inew issues a bunch of warnings when running
autoconf. Update the autoconf scripts so that they don't make a
bunch of noise anymore.

Also, when building with different users, the group file build can
fail to overwrite the group files, resulting in build failures. Fix
that, too.

Cheers,

Dave.