One or more security groups with which to associate the instances.
If your instances are launched in EC2-Classic, you can either specify
security group names or the security group IDs. For more information, see
Amazon EC2 Security Groups in the Amazon Elastic Compute Cloud
User Guide.
If your instances are launched into a VPC, specify security group IDs.
For more information, see Security Groups for Your VPC in the Amazon Virtual Private Cloud
User Guide.
Returns a reference to this object so that method calls can be chained
together.