Improve error handling in measurement register with discovery service

[MounikaBattu17]

• This contribution adheres to CONTRIBUTING.md.

What does this Pull Request accomplish?

This PR stops measurement service from starting if the measurement is not successfully registered with discovery service.

Currently, On a unsuccessful measurement register with discovery service, the exceptions are just logged and service continues to run. So to improve the error handling(not starting the measurement service on unsuccessful register), made the following changes:

1. Raised exceptions instead of returning False in register_measurement_service and unregister_service from discovery_client.py.
2. Propagated the raised exceptions to callers service_manager.py, service.py.

Tests Updates:

1. Updated unit/test_service.py to cover the exception scenario of host_service method.
2. Updated integration/test_service_manager.py to cover the exception scenario of start method.
   • Added a new fixture expect_discovery_service_error_stub return a boolean to choose from FakeDiscoveryServiceStub or FakeDiscoveryServiceStubError. By default, Return value False such that choosing FakeDiscoveryServiceStub for all test cases
   • Overridden the value to True to pick FakeDiscoveryServiceStubError for the one test cases testing exception scenario.
3. Updated test cases assert in unit/test_discovery_client.py.

Why should this Pull Request be merged?

This PR stops measurement service from starting if the measurement is not successfully registered with discovery service by raising an exception.

What testing has been done?

1. Added new tests to cover the exception scenarios and verified existing and new tests pass by running poetry run pytest.
2. Ran sample measurement example and verified the below scenarios,

• Sample measurement successfully registered with discovery service -> Able to run the measurement without any error
• Sample measurement not successfully registered with discovery service (removed measurementlink json file) -> measurement is not started and throwed an error

Traceback (most recent call last):
  File "measurementlink-python\ni_measurementlink_service\_internal\discovery_client.py", line 125, in register_measurement_service
    register_response = self.stub.RegisterService(request)
  File "measurementlink-python\ni_measurementlink_service\_internal\discovery_client.py", line 84, in stub
    address = _get_discovery_service_address()
  File "measurementlink-python\ni_measurementlink_service\_internal\discovery_client.py", line 220, in _get_discovery_service_address
    _ensure_discovery_service_started(key_file_path)
  File "measurementlink-python\ni_measurementlink_service\_internal\discovery_client.py", line 232, in _ensure_discovery_service_started
    exe_file_path = _get_discovery_service_location()
  File "measurementlink-python\ni_measurementlink_service\_internal\discovery_client.py", line 240, in _get_discovery_service_location
    registration_json_obj = json.loads(registration_json_path.read_text())
  File "Python\Python38\lib\pathlib.py", line 1236, in read_text        
    with self.open(mode='r', encoding=encoding, errors=errors) as f:
  File "Python\Python38\lib\pathlib.py", line 1222, in open
    return io.open(self, mode, buffering, encoding, errors, newline,
  File "Python\Python38\lib\pathlib.py", line 1078, in _opener
    return self._accessor.open(self, flags, mode)
FileNotFoundError: [Errno 2] No such file or directory: 'C:\\Program Files\\National Instruments\\Shared\\MeasurementLink\\MeasurementLinkService.json'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/measurementlink-python/examples/sample_measurement/measurement.py", line 113, in <module>
    main()
  File "measurementlink-python\examples\sample_measurement\.venv\lib\site-packages\click\core.py", line 1130, in __call__
    return self.main(*args, **kwargs)
  File "measurementlink-python\examples\sample_measurement\.venv\lib\site-packages\click\core.py", line 1055, in main
    rv = self.invoke(ctx)
  File "measurementlink-python\examples\sample_measurement\.venv\lib\site-packages\click\core.py", line 1404, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "measurementlink-python\examples\sample_measurement\.venv\lib\site-packages\click\core.py", line 760, in invoke
    return __callback(*args, **kwargs)
  File "/measurementlink-python/examples/sample_measurement/measurement.py", line 108, in main
    with sample_measurement_service.host_service():
  File "measurementlink-python\ni_measurementlink_service\measurement\service.py", line 388, in host_service
    raise e
  File "measurementlink-python\ni_measurementlink_service\measurement\service.py", line 379, in host_service
    self.grpc_service.start(
  File "measurementlink-python\ni_measurementlink_service\_internal\service_manager.py", line 111, in start
    raise e
  File "measurementlink-python\ni_measurementlink_service\_internal\service_manager.py", line 105, in start
    self.discovery_client.register_measurement_service(port, service_info, measurement_info)
  File "measurementlink-python\ni_measurementlink_service\_internal\discovery_client.py", line 140, in register_measurement_service
    raise FileNotFoundError(e.strerror, e.filename) from e
FileNotFoundError: [Errno No such file or directory] C:\Program Files\National Instruments\Shared\MeasurementLink\MeasurementLinkService.json
(sample-measurement-py3.8) PS measurementlink-python> 

[vigkre]

Approved with suggestions