Fix failing unit test by stubbing ec2.images
Fix failing unit test by stubbing ec2.images

[#116481439](https://www.pivotaltracker.com/story/show/116481439)

Signed-off-by: Lyle Franklin <31e283733c7a4b3b6cb03b95ab535671c2112bbe@pivotal.io>

cloudfoundry-incubator/bosh-aws-cpi-release,cloudfoundry-incubator/bosh-aws-cpi-release,cloudfoundry-incubator/bosh-aws-cpi-release