Adds handling to the Servers behavior when no security group config is provided

* Handles the case of when no security group configuration is provided to the
  servers behavior. The Compute compoisite will always at least provide an
  empty config, but people not using the composite were having errors
  due to assuming that the config was passed into the constructor

Change-Id: I31b34f4d292534f06ee888fad2873c2387a395fb
Merge "Adds handling to the Servers behavior when no security group config is provided"