Docstring for a few of the methods are not parsable

[SinaChavoshi]

Docstring for a few of the methods under aiplatform are not parsable, which breaks API doc generation and parsing tools. For example in training_jobs.py the docstring

    def _raise_failure(self):
        """Helper method to raise failure if TrainingPipeline fails.

        Raises:
            RuntimeError If training failed.
        """

should be changed to

    def _raise_failure(self):
        """Helper method to raise failure if TrainingPipeline fails.

        Raises:
            RuntimeError: If training failed.
        """