[fix] Use BaseSubnetDivisionRuleType.get_max_subnet order by subnet #728

[pandafy]

BaseSubnetDivisionRuleType.get_max_subnet will order queryset using
the "subnet" field when PostgreSQL database backend is used. Otherwise,
it will fallback to using "created" field for ordering.

Closes #728

[coveralls]

Coverage increased (+0.0002%) to 98.745% when pulling 58d8e45 on issues/728-get-max-subnet into 2b97872 on master.

[nemesifier]

Any idea of what is happening to the test coverage?

[nemesifier]

Please try combining these changes with the changes in openwisp/openwisp-users#340 (move flags to rc file and run tests in parallel), in the second call to coverage, in order to avoid increasing the build time excessively, we could run only the tests of the subdivision app, in this case --keepdb should help speed up things a bit.

POSTGRESQL=1 coverage run /tests/manage.py test openwisp_controller.subnet_division.tests

It should work!

[pandafy]

When using POSTGRESQL=1 only a subset of tests are executed. The abstraction is done in runtests.py to allow running the tests locally as well.

openwisp-controller/runtests.py

Lines 25 to 26 in d25b16c

	if os.environ.get('POSTGRESQL', False):
	args.extend(['--tag', 'db_tests'])