MCO-292 Fix for `missing dist macro` for RedHat packages

The plugin application incorrectly set package dependencies for RedHat
variants; as a consequence, rpm failed to install the built packages.

This change fixes the above issue (regression of MCO-285) by adding the
release label (e.g. ".el6") to package dependencies.
Tested on a CentOS box by installing mcollective-process-agent.