createS3Bucket does not strip the s3:// prefix

Assuming `AWS_S3_BUCKET_NAME` is something like `s3://my-bucket`, then `bucketS3Uri=s3://s3://my-bucket`:
```
    local bucketS3Uri="s3://$AWS_S3_BUCKET_NAME"
```
(https://github.com/frekele/helicopterizer/blob/master/scripts/core/helper.sh#L198)

This should be:
```
    local bucketName=$(removeS3Prefix $AWS_S3_BUCKET_NAME)
```

I will make a PR when I can.