public RepositoryVersionEntity getSourceRepositoryVersion(String serviceName) {
    return m_sourceRepositoryMap.get(serviceName);
  }
Gets the version that service is being considered to be "coming from".
<p/>
With a {@link Direction#UPGRADE}, this value represent the services'
desired repository. However, {@link Direction#DOWNGRADE} will use the same
value for all services which is the version that the downgrade is coming
from.

@return the source repository for the upgrade
ambari-server/src/main/java/org/apache/ambari/server/stack/upgrade/orchestrate/UpgradeContext.java