Specify required "Principal" field to make TF happy
Specify required "Principal" field to make TF happy

[#137807277](https://www.pivotaltracker.com/story/show/137807277)

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