Share buildDir for android/soong/android tests

There is no need to create a separate buildDir for each test
file, use TestMain to create a global one for the package.

Test: all soong tests
Change-Id: I435ee7aa88b7e0bb8ccc1ba79f82833a7accf3e9
diff --git a/android/prebuilt_etc_test.go b/android/prebuilt_etc_test.go
index d977c30..0a2c7a4 100644
--- a/android/prebuilt_etc_test.go
+++ b/android/prebuilt_etc_test.go
@@ -15,16 +15,13 @@
 package android
 
 import (
-	"io/ioutil"
-	"os"
 	"path/filepath"
 	"reflect"
 	"testing"
 )
 
 func testPrebuiltEtc(t *testing.T, bp string) (*TestContext, Config) {
-	config, buildDir := setUp(t)
-	defer tearDown(buildDir)
+	config := TestArchConfig(buildDir, nil)
 	ctx := NewTestArchContext()
 	ctx.RegisterModuleType("prebuilt_etc", ModuleFactoryAdaptor(PrebuiltEtcFactory))
 	ctx.RegisterModuleType("prebuilt_etc_host", ModuleFactoryAdaptor(PrebuiltEtcHostFactory))
@@ -51,20 +48,6 @@
 	return ctx, config
 }
 
-func setUp(t *testing.T) (config Config, buildDir string) {
-	buildDir, err := ioutil.TempDir("", "soong_prebuilt_etc_test")
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	config = TestArchConfig(buildDir, nil)
-	return
-}
-
-func tearDown(buildDir string) {
-	os.RemoveAll(buildDir)
-}
-
 func TestPrebuiltEtcVariants(t *testing.T) {
 	ctx, _ := testPrebuiltEtc(t, `
 		prebuilt_etc {