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/android/androidmk_test.go b/android/androidmk_test.go
index a558f45..10527b9 100644
--- a/android/androidmk_test.go
+++ b/android/androidmk_test.go
@@ -80,10 +80,10 @@
 	config := TestConfig(buildDir, nil, bp, nil)
 	config.inMake = true // Enable androidmk Singleton
 
-	ctx := NewTestContext()
+	ctx := NewTestContext(config)
 	ctx.RegisterSingletonType("androidmk", AndroidMkSingleton)
 	ctx.RegisterModuleType("custom", customModuleFactory)
-	ctx.Register(config)
+	ctx.Register()
 
 	_, errs := ctx.ParseFileList(".", []string{"Android.bp"})
 	FailIfErrored(t, errs)
@@ -252,10 +252,10 @@
 		config := TestConfig(buildDir, nil, testCase.bp, nil)
 		config.inMake = true // Enable androidmk Singleton
 
-		ctx := NewTestContext()
+		ctx := NewTestContext(config)
 		ctx.RegisterSingletonType("androidmk", AndroidMkSingleton)
 		ctx.RegisterModuleType("custom", customModuleFactory)
-		ctx.Register(config)
+		ctx.Register()
 
 		_, errs := ctx.ParseFileList(".", []string{"Android.bp"})
 		FailIfErrored(t, errs)