generic: add test for fsync after renaming directory

generic: add test for fsync after renaming directory

Test that if we rename a directory, create a new file or directory that
has the old name of our former directory and is a child of the same
parent directory, fsync the new inode, power fail and mount the
filesystem, we see our first directory with the new name and no files
under it were lost.

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>