Standardizing spec tests

Since the `to_s` has been fixed for Razor::Command, the standard for spec tests should be `describe Razor::Command::$command_name do...`. This removes a redundancy too in `it_behaves_like "a command"`.

Fixes https://tickets.puppetlabs.com/browse/RAZOR-240
Handle cases where command's attribute has no datatype

Fixes https://tickets.puppetlabs.com/browse/RAZOR-268
Wrong error for multiple create-broker commands

Running `create-broker` multiple times with the
same arguments was causing the broker types to
be compared incorrectly. This corrects that behavior.

Fixes https://tickets.puppetlabs.com/browse/RAZOR-251
Release 0.15.0