Make AMI id configurable via BOSH_AWS_IMAGE_ID
Make AMI id configurable via BOSH_AWS_IMAGE_ID

* Also make the default values to both 64-bit

Signed-off-by: Phan Le <f2c5995718b197bbd6f63c99e8aab6ee2af1c495@pivotal.io>

tracyde/bosh-aws-cpi-release,cloudfoundry-incubator/bosh-aws-cpi-release,jfuerth/bosh-aws-cpi-release,wcamarao/bosh-aws-cpi-release,jfuerth/bosh-aws-cpi-release,wcamarao/bosh-aws-cpi-release,tracyde/bosh-aws-cpi-release,cloudfoundry-incubator/bosh-aws-cpi-release,cloudfoundry-incubator/bosh-aws-cpi-release,wcamarao/bosh-aws-cpi-release,tracyde/bosh-aws-cpi-release,jfuerth/bosh-aws-cpi-release