When trying to deploy a serverless service that does not currently deploy correctly onto localstack using a custom deployment bucket, the lambdas seems to be created regardless (???) but not as part of the stack, with localstack outputting `botocore.errorfactory.ResourceConflictException: An error occurred (ResourceConflictException) when calling the CreateFunction operation: Function already exist` .

For example, the `serverless.yml` below would currently fail to deploy due to  #1676 , but because a `deploymentBucket` was added, it will instead fail due to `Function already exist`. Subsequently removing `deploymentBucket` or even `events` from the the file will not allow it to deploy - it will fail until localstack is restarted ( or until the lambda is manually deleted?).

I've also reproduced this with services suffering from #1675. 

```yaml
service: "localtest"

provider:
  name: "aws"
  runtime: "nodejs10.x"
  deploymentBucket:
    name: "testbucket"

functions:
  hello:
    handler: "handler.hello"
    events:
      - schedule: "cron(0 * * * ? *)"

plugins:
- "serverless-localstack"

custom:
  localstack:
    stages:
      - "local"
```
stack_name = self._get_param('StackName')
        stack = self.cloudformation_backend.get_stack(stack_name)
        logical_resource_id = self._get_param('LogicalResourceId')
        if not stack:
            msg = ('Unable to find CloudFormation stack "%s" in region %s' %
                   (stack_name, aws_stack.get_region()))
            if aws_stack.get_region() != self.region:
                msg = '%s/%s' % (msg, self.region)
            LOG.warning(msg)
            response = aws_responses.flask_error_response(msg, code=404, error_type='ResourceNotFoundException')
            return 404, response.headers, response.data
        for stack_resource in stack.stack_resources:
            
            
            if stack_resource and stack_resource.logical_resource_id == logical_resource_id:
                resource = stack_resource
                break
        else:
            raise ValidationError(logical_resource_id)
        template = self.response_template(
            responses.DESCRIBE_STACK_RESOURCE_RESPONSE_TEMPLATE)
        return template.render(stack=stack, resource=resource)
    responses.CloudFormationResponse.describe_stack_resource = describe_stack_resource
def inject_stats_endpoint():
    """ Inject a simple /_stats endpoint into the moto server backend Web app. """
    
    from moto import server as moto_server
    def _get_stats():