Added bats integration tests to verify that users can send mail via ssmtp

- Used a pre-release version of the mailtrap gem built from [this pull
   request][1] off of [trinitronx/mailtrap@develop][2]
 - Added Fedora box to test kitchen
 - Tested with [yum cookbook][3] with bugfix for [COOK-3290][4]
 - All test kitchen tests passing!

[1]: https://github.com/mmower/mailtrap/pull/7
[2]: https://github.com/trinitronx/mailtrap/tree/develop
[3]: https://github.com/opscode-cookbooks/yum/pull/52
[4]: http://tickets.opscode.com/browse/COOK-3290