[Chapel Merge] Add a -python2 flag to nightly and use it for pyth

Branch: refs/heads/master
Revision: 07aea7b
Author: e-kayrakli
Log Message:

Merge pull request #16738 from e-kayrakli/change-python-test-version

Add a -python2 flag to nightly and use it for python 2.7 testing

We are now using python 3 for our testing. Where before that change we were
running examples testing using python 3. This PR swaps that job to use python
2.7 for backward compatibility.

To enable that this PR adds -python2 flag to nightly, and uses that to avoid
bunch of scripts just in case, and runs make check only.

[Reviewed by @ronawho]

Modified Files:
A util/cron/test-linux64-python27.bash
R util/cron/test-linux64-python3.bash
M util/cron/nightly

Compare: https://github.com/chapel-lang/chapel/compare/52461c905fbc...07aea7b6e1ef