testutils/patch.py: Add methods for applying and removing patches

import subprocess

def apply(file, patch):

    try:

        subprocess.check_output(['patch', file, patch])

    except subprocess.CalledProcessError as e:

        message = "Patch failed with exit code {}\n Output:\n {}".format(

            e.returncode, e.output)

        print(message)

        raise

def remove(file, patch):

    try:

        subprocess.check_output(['patch', '--reverse', file, patch])

    except subprocess.CalledProcessError as e:

        message = "patch --reverse failed with exit code {}\n Output:\n {}".format(

            e.returncode, e.output)

        print(message)

        raise