fstests: generic test for fsync after removing xattrs

fstests: generic test for fsync after removing xattrs

This test is motivated by an fsync issue discovered in btrfs.
The issue was that the fsync log replay code did not remove xattrs that
were deleted before the inode was fsynced. The result was unexpected
and differed from xfs and ext3/4 for example.

The btrfs issue was fixed by the following linux kernel patch:

   Btrfs: remove deleted xattrs on fsync log replay

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>