Indicates whether this option group can be applied to both VPC and non-VPC
instances. The value true indicates the option group can be
applied to both VPC and non-VPC instances.
If AllowsVpcAndNonVpcInstanceMemberships is false, this
field is blank. If AllowsVpcAndNonVpcInstanceMemberships is
true and this field is blank, then this option group can be
applied to both VPC and non-VPC instances. If this field contains a value,
then this option group can only be applied to instances that are in the VPC
indicated by this field.