Add pymongo, a dep of mongodb_user ansible module

[cognifloyd]

This adds a stub tasks file for adding auth to mongo. Currently, it is not imported/included anywhere. We'll only include/import this once we're satisfied that it is complete and ready to use. The only task in this stub file so far is adding pymongo, a dep of the mongodb_user ansible module.

Ansible docs mention (in the comment to an example near the end) that pymongo 2.5+ is supported, so system level packages work for all platforms.

• CentOS 6 -> EPEL -> python-pymongo-2.5.2
• CentOS 7 -> EPEL -> python-pymongo-2.5.2
• Ubuntu 14.04 -> python-pymongo_2.6.3
• Ubuntu 16.04 -> python-pymongo_3.2