MCO-285 Fix for `mco plugin package` on RedHat variants

The plugin application failed to including the RedHat label to the
package name.

This fixes the issue by correctly adding the name and refering to the
proper file path; note that based on the following web page, it's safe
to assume that all the RedHat release labels start with a dot:
http://fedoraproject.org/wiki/Packaging:DistTag#Possible_values_for_.25.7Bdist.7D

The fix was based on the patch suggested by Daniel Schleenzig.