Pass Config to NewTestContext instead of ctx.Register

Prepare for using Config when adding singletons by passing
Config to NewTestContext and NewContext instead of to ctx.Register.
This will enable a followup change to store SingletonMakeVarsProviders
registered on the Context in the Config, which is necessary to run
multiple tests in parallel without data races.

Test: all soong tests
Change-Id: Id229629a4e42ff4487d317241673837726c075fc
diff --git a/genrule/genrule_test.go b/genrule/genrule_test.go
index fdbb9d9..c19078f 100644
--- a/genrule/genrule_test.go
+++ b/genrule/genrule_test.go
@@ -53,14 +53,14 @@
 
 func testContext(config android.Config) *android.TestContext {
 
-	ctx := android.NewTestArchContext()
+	ctx := android.NewTestArchContext(config)
 	ctx.RegisterModuleType("filegroup", android.FileGroupFactory)
 	ctx.RegisterModuleType("tool", toolFactory)
 
 	registerGenruleBuildComponents(ctx)
 
 	ctx.PreArchMutators(android.RegisterDefaultsPreArchMutators)
-	ctx.Register(config)
+	ctx.Register()
 
 	return ctx
 }