fstests: initial bcachefs support

fstests: initial bcachefs support

To get started, you'll need to get bcachefs from the kernel repository
  https://evilpiepirate.org/git/bcachefs.git/

and tools from
  https://evilpiepirate.org/git/bcache-tools.git/

Build kernel as normal, enabling CONFIG_BCACHEFS_FS (and probably
CONFIG_BCACHEFS_DEBUG), and build and install tools. Then running
fstests is exactly the same as other local filesystems - just set
FSTYP=bcachefs

Also see https://evilpiepirate.org/git/ktest.git/ for a tool for
conveniently building kernel and running fstests inside a qemu VM.

This patch also updates generic/441 to run the more thorough test on
bcachefs, and generic/425 to not run on bcachefs (since bcachefs does
not store xattrs in blocks)

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>