@Override
  public int hashCode() {
    int result;
    result = 31 + getExtensionName().hashCode();
    return result;
  }
An extension version is like a stack version but it contains custom services.  Linking an extension
version to the current stack version allows the cluster to install the custom services contained in
the extension version.
ambari-server/src/main/java/org/apache/ambari/server/controller/ExtensionResponse.java