code: public ConsulResponse<List<CatalogService>> getService(final String serviceName,
                                                             final String datacenter, final String tag
      ) {
          return getService(serviceName, datacenter, tag, RequestOptions.BLANK);
      }
docs: Retrieves a single service for a given datacenter.
  <p>
  GET /v1/catalog/service/{service}?dc={datacenter}
  
  @param serviceName service name
  @param datacenter  datacenter
  @param tag         tag
  @return A {@link io.advantageous.consul.domain.ConsulResponse} containing
  {@link io.advantageous.consul.domain.CatalogService} objects.