Support testing Rules in Modules and Rules and Builds in Singletons

Add support for TestingModule to return RuleParams for rules created
by the module.

Refactor TestingModule to use helpers, and use the helpers to
implement a similar TestingSingleton.

Use the new functionality to test RuleBuilder's module and singleton
rules.

Test: none
Change-Id: I8348c56ff5086d0c49401f5a00faf7c864e6b6f3

android/register.go

@@ -61,7 +61,7 @@ func SingletonFactoryAdaptor(factory SingletonFactory) blueprint.SingletonFactor
 		if makevars, ok := singleton.(SingletonMakeVarsProvider); ok {
 			registerSingletonMakeVarsProvider(makevars)
 		}
-		return singletonAdaptor{singleton}
+		return &singletonAdaptor{Singleton: singleton}
 	}
 }