fs: add generic osd fs selector stubs

Signed-off-by: Sage Weil <sage@inktank.com>
make btrfs.yaml a symlink
make ext4.yaml a symlink
make xfs.yaml a symlink
btrfs: enable sloppy crc
xfs: enable sloppy crc
fs/samba: reenable smbtorture lock test

It passes now that #5025 is fixed, yay!

Signed-off-by: Sage Weil <sage@inktank.com>