The ImageCollectionTest.test_pull_multiple test performs a `docker pull` without
a `:tag` specified) to pull all tags of the given repository (image).

After pulling the image, the image(s) pulled are checked to verify if the list
of images contains the `:latest` tag.

However, the test assumes that all tags of the image are tags for the same
version of the image (same digest), and thus a *single* image is returned, which
is not always the case.

Currently, the `hello-world:latest` and `hello-world:linux` tags point to a
different digest, therefore the `client.images.pull()` returns multiple images:
one image for digest, making the test fail:

=================================== FAILURES ===================================
____________________ ImageCollectionTest.test_pull_multiple ____________________
tests/integration/models_images_test.py:90: in test_pull_multiple
assert len(images) == 1
E AssertionError: assert 2 == 1
E + where 2 = len([<Image: 'hello-world:linux'>, <Image: 'hello-world:latest'>])

This patch temporarily skips the broken test until it is fixed upstream.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>