Python3: replace `distutils` with `sysconfig`

Python3: replace `distutils` with `sysconfig`

- `distutils` module is long time deprecated and already deleted
  from the CPython mainline.

- To remain compatible with Debian/Ubuntu Python3 packaging style,
  try
  `distutils.sysconfig.get_python_path(0,0)`
  first with fallback on
  `sysconfig.get_path('purelib')`

- pyzfs_unittest suite is run unconditionally as a part of ZTS.

- Add pyzfs_unittest suite to sanity tests.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: szubersk <szuberskidamian@gmail.com>
Closes #12833
Closes #13280
Closes #14177