Use embedded MongoDB for running the tests

This improves test predictability by ensuring the tests are always run with the same version of MongoDB instead of whatever random version happens to be installed on the current host

@roughy took your pull request https://github.com/devbliss/mongojack/pull/43 and updated it so that it would work in both Maven and Eclipse. Let me know if this looks okay to you as I would like to merge it soon
please add contribution information
https://github.com/devbliss/mongojack/blob/master/CONTRIBUTING.md#making-changes