code: public Observable<String> getMetadataAsync(String scope) {
          return getMetadataWithServiceResponseAsync(scope).map(new Func1<ServiceResponse<String>, String>() {
              @Override
              public String call(ServiceResponse<String> response) {
                  return response.body();
              }
          });
      }
docs: Gets OData metadata XML document.
  
  @param scope A valid scope, i.e. management group, subscription, resource group, or resource ID. Scope used has no effect on metadata returned.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the String object