roachtest/django: miscellaneous changes

[otan]

We do this for /mnt/data1/django, so do django-cockroach too, just in
case. Not sure if it'll do anything, but just in case.

Refs: #80614

Release note: None

[cockroach-teamcity]

This change is 

[timgraham]

I'm not sure if there's a reason why the repo needs to be cloned in the first place. I would advocate to replace the clone and install with pip install django-cockroachdb 4.0.x to always get the latest version from PyPI.

There are a couple of other obsolete things in this file that I noticed, namely RUNNING_COCKROACH_BACKEND_TESTS=1 and --parallel 1 are no longer needed.

[otan]

does pip install django-cockroachdb 4.0.x also bring the tests in?

i can remove the extraneous flags though.

[timgraham]

The test suite is in the Django repo, not in django-cockroachdb.

[otan]

pip install django-cockroachdb 4.0.x

doesn't seem to work:

		Wraps: (5) pip3 install django-cockroachdb 4.0.x returned
		  | stderr:
		  | ERROR: Could not find a version that satisfies the requirement 4.0.x (from versions: none)
		  | ERROR: No matching distribution found for 4.0.x
		  |
		  | stdout:
		  | Defaulting to user installation because normal site-packages is not writeable
		  | Collecting django-cockroachdb
		  |   Using cached django_cockroachdb-4.0.1-py3-none-any.whl (25 kB)

[timgraham]

Sorry, that should be: pip install django-cockroachdb==4.0.*

[ZhouXing19]

Thanks!

[otan]

bors r+

[craig]

Build succeeded:

• GitHub CI (Cockroach)