generic: add test for fsync after renaming file

generic: add test for fsync after renaming file

Test that if we rename a file, create a new file that has the old name
of the other file and is a child of the same parent directory, fsync the
new inode, power fail and mount the filesystem, we do not lose the first
file and that file has the name it was renamed to.

This test is motivated by an issue found in btrfs which is fixed by the
following patch for the linux kernel:

  "Btrfs: fix file loss caused by fsync after rename and new inode"

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>