[bug] Template loader incorrect order in tests settings

[asmodehn]

Describe the bug

As discussed in openwisp/openwisp-controller#1202 , the order of template loaders in test settings seems incorrect.
This dates back to e3577f0, it seems intentional.

I ll try to come up with a PR, to see what changes if the order of loaders change... and if I can come up with a different solution...

[asmodehn]

So I checked the doc and the order is indeed correct as per the documentation... but that order is not consistent throughout openwisp packages, or the documentation, and seem to trigger issues with template resolution.

I m starting to thing this is due to a mix (at least in this repository) between:

• the "django way" of overriding a template (ie. put the override app in INSTALLED_APPS, before the original app), as openwisp_users does with django.contrib.admin,
• and the "openwisp way" (remove the original app from INSTALLED_APPS, put it in EXTENDED_APPS instead, and add the override app in INSTALLED_APPS) as would a sample_users app do.

That means that the django.template.loaders.app_directories.Loader will find the login template in django.contrib.admin if placed before openwisp_utils.loaders.DependencyLoader in the case of sample_users.

The correct template was moved from INSTALLED_APPS to EXTENDED_APPS => Loader order will determine which one is found)