We have a deprecate method, lets use it

Signed-off-by: Moses Mendoza <moses@puppetlabs.com>
Add an is_rc? utility method and use it

This method will return whether or not this is an RC version based on the
string returned by get_dash_version. We use it in building rpms and debs to
determine the status of our build, e.g. rc vs foss.

Signed-off-by: Moses Mendoza <moses@puppetlabs.com>