Remove reference to ConfigParser object in ModuleRegistry. Instead:
* make use of JJBConfig.get_module_config to grab settings for Hipchat
Notifier Plugin
* make use of JJBConfig.yamlparser['allow_empty_variables'] rather
than repeating ConfigParser logic moved out of the YamlParser into
JJBConfig in an earlier commit.
Change-Id: Icb7ef514826005545e48af993335ce120f973b0d