Initial boot of RHEL CoreOS failing in AWS if network access is restricted in OpenShift Container Platform 4

Issue

• When using S3 source, and network isn't ready for its first metadata retrieval, the regionHint is nil and so defaults to us-east-1.
• Bootstrap node fails downloading the ignition fragment from s3, while s3-eu-central-1 prefix lists are accessible. We can see in the logs that Ignition component tries to reach S3 in us-east-1 and therefore is failing as access to this network is not allowed and blocked by the VPC.