xfs: test xfsprogs log formatting infrastructure

xfs: test xfsprogs log formatting infrastructure

The xfsprogs libxfs layer implements its own log formatting code to
support utilities that might need to format the log, such as mkfs,
repair, metadump, etc. This code is fairly independent from kernel log
writing code. Therefore, add a test that reformats the log from
userspace with various supported log stripe unit alignments and verifies
that the end result is a correctly formatted log.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>