ZTS: add existing tests to runfiles
Some test cases were committed to the repository but never added to
runfiles.
Move zfs_unshare_008_pos to the Linux-only runfile.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: szubersk <szuberskidamian@gmail.com>
Closes #14701