Fix profile tests' warnings if postmap binary not installed

This PR improves the developer experience when running tests (especially profile tests).

Currently, `python manage.py test profile` has a number of passing tests that output messages to the console. These messages ("`/etc/postfix/virtual_alias_maps` not found") are due to the postmap binary not being installed on the local test system (see Advanced Installation docs).

I've commented out a few lines that were flagged to be fixed in `__init__.py` and skipped the test for the binary in the `profile/tests.py` file.

It would be good to fix this more elegantly and perhaps refactor the very long test file after the Django upgrade is completed. 


Seems reasonable, but why does the mock.patch macro need to be commented out?