1175512 - Fixes mongoengine database args to use correct database

The issue is that the pulp setting `seeds` was being used as the database name. It connected to MongoDB because the mongoengine defaults for host and port are the same as pulp and MongoDB. I also reviewed all the connection parameters and consolidated authentication with how mongoengine expects it. I then updated all the tests which I believe cover all the necessary cases.

This was continuing to use the correct database name for non mongoengine models because they use PulpCollection which is where the existing Pulp code specifies the database name. What we're doing with mongoengine is much simpler so that is good.

I hand tested that the existing non mongoengine collections will continue to auto create and use the correct database.

This adjusts the mongoengine connection to work with one seed. Multi-seed testing is [a different issue](https://rally1.rallydev.com/#/7675694122d/detail/userstory/26229270474) that should be looked at soon. Mongoengine needs more testing with multi-seed configurations to do it effectively.

I also ran the [tests on all platforms and it passed](https://pulp-jenkins.rhev-ci-vms.eng.rdu2.redhat.com/job/unittest-pulp/52/).