ServiceRegistration is a data object containing information regarding a
"peer" service within a "composite" service. The Composite service utilizes
or controls multiple peer services. In order to do so it needs an internal
key used only by the composite service. With this key the composite gets a
reference to the peer. In some situations it will be necessary to use a peer
with a different name. reserveAs is a method which will re-bind the composite
to a differently named peer service.