Add a script for generating a collage of provider logo files.

This image can be used on the homepage and inside documentation.
Update GCE driver to API version v1beta16 Most of the changes are in the test fixtures, some were regenerated, some were just had URLs updated as necessary. In addition, there were some changes made to the tests to use the regenerated test fixtures.

Signed-off-by: Tomaz Muraus <tomaz@apache.org>
Fix long line

Signed-off-by: Tomaz Muraus <tomaz@apache.org>
Update CHANGES.
Update tox config.