Feature/adding support for trusty

This pull request adds temporary support for Ubuntu Trusty (14.04).  It does this by detecting a trusty server and downloading and installing the Ubuntu 13.10 mesosphere Mesos debian package.

Other changes in this PR include:

* Added Ubuntu 14.04 platform type.
* Updated .kitchen.ec2.yml file with a new working debian AMI.
* Introduced an additional yum based zookeeper test cookbook for setting up a standalone zookeeper server for mesos to use for testing.
* Added additional serverspec tests to ensure that mesos master and slave start and register correctly with the local zookeeper.
* Cleaned up code based on latest rubocop rules.
* Updated default Mesos version to 0.17.0