Bootstrap doesn't support --role_arn

### Description

Running `sam deploy --guided` the first time to create the S3 bucket via a CloudFormation template, the `--role_arn` parameter isn't supported in https://github.com/awslabs/aws-sam-cli/blob/master/samcli/lib/bootstrap/bootstrap.py

### Steps to reproduce

Run `sam deploy --guided` and it fails because we have policies that require all CloudFormation stacks to use a specific role.

### Observed result

Please provide command output with `--debug` flag set.

### Expected result

I'm able to run `sam deploy --guided --role_arn ` and SAM will provision it's CloudFormation stack with the role I specified.

### Additional environment details (Ex: Windows, Mac, Amazon Linux etc)

1. OS: Mac
2. `sam --version`: SAM CLI, version 0.47.0

Would you accept a pull request adding this?