Island: Don't raise errors if machine upsert did no changes

It doesn't make sense to raise an error if upsert did no changes, because the purpose of "upsert" method is to ensure that data is up-to-date. If no changes were made it means it's already up-to-date.

monkey/monkey_island/cc/repository/mongo_machine_repository.py

@@ -38,12 +38,6 @@ class MongoMachineRepository(IMachineRepository):
         except Exception as err:
             raise StorageError(f'Error updating machine with ID "{machine.id}": {err}')
 
-        if result.matched_count != 0 and result.modified_count != 1:
-            raise StorageError(
-                f'Error updating machine with ID "{machine.id}": Expected to update 1 machine, '
-                f"but {result.modified_count} were updated"
-            )
-
         if result.matched_count == 0 and result.upserted_id is None:
             raise StorageError(
                 f'Error inserting machine with ID "{machine.id}": Expected to insert 1 machine, '

monkey/tests/unit_tests/monkey_island/cc/repository/test_mongo_machine_repository.py

@@ -146,21 +146,6 @@ def test_upsert_machine__storage_error_exception(error_raising_machine_repositor
         error_raising_machine_repository.upsert_machine(machine)
 
 
-def test_upsert_machine__storage_error_update_failed(error_raising_mock_mongo_client):
-    mock_result = MagicMock()
-    mock_result.matched_count = 1
-    mock_result.modified_count = 0
-
-    error_raising_mock_mongo_client.monkey_island.machines.replace_one = MagicMock(
-        return_value=mock_result
-    )
-    machine_repository = MongoMachineRepository(error_raising_mock_mongo_client)
-
-    machine = MACHINES[0]
-    with pytest.raises(StorageError):
-        machine_repository.upsert_machine(machine)
-
-
 def test_upsert_machine__storage_error_insert_failed(error_raising_mock_mongo_client):
     mock_result = MagicMock()
     mock_result.matched_count = 0