This commit sees JJBConfig start to take the form it ought to have,
namely using attributes to represent different logical sections of
configuration that target specific subsystems of JJB.
It also moves ConfigParser data retrieval from
jenkins_jobs.modules.helpers.get_value_from_yaml_or_config_file() to
jenkins_jobs.config.JJBConfig.get_module_config()
TODO: Add JJBConfig tests to validate the behavior of JJBConfig in
specific circumstances.
Change-Id: I053d165559f5325a2f40b239117a86e6d0f3ef37