feat: Use a map for root_block_device instead of list#396

Yethal wants to merge 2 commits intoterraform-aws-modules:masterterraform-aws-modules/terraform-aws-ec2-instance:masterfrom

Yethal:root_block_device_objectYethal/terraform-aws-ec2-instance:root_block_device_objectCopy head branch name to clipboard