fix test coverage for the API project

[terrazoon]

the API project test coverage was ignoring all code in notifications-utils. Previously we had a separate notification-utils project in GitHub that ran its own tests. Now that notifications-utils is integrated into notifications-admin, we should run coverage on notifications-utils.

The API project was also counting coverage against all code under tests/, which makes no sense.

When we run coverage properly (ignore migrations and tests, count everything else), it turns out we only have 91% coverage. We need to bring this back up to 95%.

[terrazoon]

Brought it up from 91 to 93 for this sprint (Sleipnir). Putting it back in queue to finish next sprint