public interface LocationDefinition
getSpec() is like a serialized representation
 of the location so that Brooklyn can create a corresponding location.
 
 Examples include a complete description (e.g. giving a list of machines in a pool), or
 a name that matches a named location defined in the brooklyn poperties.
 
 Users are not expected to implement this, or to use the interface directly. See
 LocationRegistry.resolve(String) and ManagementContext.getLocationRegistry().