Add support for the command alias (Cmnd_Alias) directive

This adds support for building a set of command aliases to use in your
sudoers file. In addition, the test kitchen tests were enhanced to
ensure the new functionality behaves as expected.

The Cmnd_Alias directive, in short, allows you to specify a list of
commands to allow (or disallow). You then provide this command alias
an entry in your commands Array. The alias name should be capitalized-
alphanumeric and may contain underscores[1].

**NOTE** It appears that the tests on master are currently failing
due to a new version of Rubocop. I will be working on a patch to fix
the Rubocop tests. However, tests for this branch will fail.

[1] http://www.sudo.ws/sudoers.man.html#x416c6961736573