Salt: [BUG] [RC1 Sodium] python 2 deprecation warnings and halt salt-call

[sagetherage]

Description
Missed deprecation warnings:

https://github.com/saltstack/salt/blob/master/salt/scripts.py#L106 and https://github.com/saltstack/salt/blob/master/salt/scripts.py#L215-L227

[waynew]

Per discussion in the Community Slack, allowing people to even start Salt with Python2 is just a bad idea and will cause long-term confusion. We're going to change these to a sys.exit line, with some verbage to the effect of:

ERROR: Python 2 is no longer supported in Salt. Please upgrade to Python 3 to continue receiving updates to Salt.

[waynew]

I believe we should also halt on salt-call

[waynew]

FWIW, we've changed basically all of the collections.abc imports, so now nothing will run on Python2, it will just fail with an exception - it would be ideal to make it not do that.