Move env var validation to the top
Move env var validation to the top

Otherwise we get strange errors from unset project_id:
	(erb):24:in `<main>': undefined method `split' for nil:NilClass (NoMethodError)

cloudfoundry-incubator/bosh-google-cpi-release,evandbrown/bosh-google-cpi-release,evandbrown/bosh-google-cpi-release,evandbrown/bosh-google-cpi-release,cloudfoundry-incubator/bosh-google-cpi-release,evandbrown/bosh-google-cpi-release,cloudfoundry-incubator/bosh-google-cpi-release,cloudfoundry-incubator/bosh-google-cpi-release