message: Added option to init noise model by Json string
  Needed for TNQVM tests
diff: @@ -210,10 +210,19 @@ void IbmqNoiseModel::initialize(const HeterogeneousMap &params) {
  m_gateErrors.clear();
  m_gateDurations.clear();
  m_roErrors.clear();
  + // Note: we support both remote backend JSON and cache JSON string.
  + // So that we can test this with offline JSON.
  + if (params.stringExists("backend") || params.stringExists("backend-json")) {
  + const auto backendJsonStr = [&]() {
  if (params.stringExists("backend")) {
  auto ibm = xacc::getAccelerator("ibm:" + params.getString("backend"));
  auto props = ibm->getProperties().get<std::string>("total-json");
  - auto backEndJson = nlohmann::json::parse(props);
  + return props;
  + }
  + return params.getString("backend-json");
  + }();
  +
  + auto backEndJson = nlohmann::json::parse(backendJsonStr);
  // Parse qubit data:
  auto qubitsData = backEndJson["qubits"];
  size_t nbQubit = 0;
  