illumos gate

Tested running each of:

• mapfilechk
• wsdiff
• cddlchk
• git-pbchk
• hdrchk
• wscheck
• crightchk.py
• validate_pkg

under Python 3.9, 3.7 and 2.7

Confirmed that even 2.7 supports the new threading.is_alive() method, the previous isAlive() being formally deprecated in 3.8 and removed in 3.9

(The wsdiff test confirms this but just for completeness):

Python 2.7.18 (default, Oct 11 2020, 16:42:09)
[GCC 9.3.0] on sunos5
Type "help", "copyright", "credits" or "license" for more information.
>>> import time, threading
>>> def worker(): time.sleep(3600)
...
>>> t = threading.Thread(target=worker)
>>> t.isAlive()
False
>>> t.is_alive()
False
>>> t.start()
>>> t.isAlive()
True
>>> t.is_alive()
True
>>>

Check that python3.9 /usr/lib/zfs/pyzfs.py operates,
also import libbe_py under python3.9, and I have also tested that a full pkg update works with python 3.9 including BE creation and activation.

A full gate build with python 3.9 has also been done which exercises validate_pkg and friends.