The stack is now set up in one place.
The S3 bucket isn't created on create if a bucket is already specified.
Working on configurability for the developer.
There is still the possibility of failing to deploy the stack
if the iamRoleArn is set, and a deploymentBucket is specified
So that the custom provider resources are not stored in a temp variable.
Furthermore the whole CloudFormation content is available in this.serverless.service.resources.