generic: test partial block device failure

generic: test partial block device failure

Calls like fsync() should report failure on partial I/O failure, e.g. a
single failed disk in a raid 0 stripe.

This test is motivated by an XFS bug, and this commit fixed the issue
xfs: return errors from partial I/O failures to files

This case is written by David Jeffery <djeffery@redhat.com> originally.

Signed-off-by: Eryu Guan <eguan@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>