Replace MongoDB dependency

[mariussturm]

Currently the tests are failing with:

TASK [elastic.elasticsearch : set_fact] ****************************************

fatal: [localhost]: FAILED! => {"failed": true, "msg": "'redhat_elasticsearch_install_from_repo' is undefined"}   

I think this is because of the Ansible version we use for running the tests. Elasticsearch needs Ansible version >= 2.2.0 and the test suite uses 2.1.

For updating the test suite to 2.2 we need a MongoDB role that is compatible with it.

https://github.com/lesmyrmidons/ansible-role-mongodb unfortunately doesn't work. Since a fix is on master but never pushed to Galaxy I consider that role as unmaintained.

So to get out of this we need a maintained MongoDB role that supports Ansible 2.2 as well as Debian/Ubuntu platform and RedHat/Centos.

[mariussturm]

To get the tests green again we use the master branch of the current MongoDB role and provide a requirements.yml that works with Ansible 2.1.2 and 2.2.1 #67
From there on we can research other MongoDB solutions.

[malcyon]

I tried using this role, but it doesn't work on CentOS 7:

https://github.com/UnderGreen/ansible-role-mongodb

It seems like there aren't a lot of good MongoDB roles out there. I'm guessing that's why we install it ourselves.

[malcyon]

This looks promising:

https://github.com/ansible-collections/community.mongodb