Output apkcerts file for android_app_set.

Soong and Make have no ways to figure out what splits will be outputted
from a given android_app_set, so it's impossible for them to provide
full PACKAGES.$(LOCAL_MODULE).CERTIFICATE entries, which are required to
build a final apkcerts.txt. This change makes extract_apks produce
apkcerts.txt files for each input modules instead. The Make-side
counterpart of this change merges all local apkcerts.txt into a final
one.

Fixes: 160119159
Test: main_test.go
Test: m apkcerts-list
Merged-In: I321e80fd636a955213761f56a3ac64bfe7f7f7c0
Change-Id: I321e80fd636a955213761f56a3ac64bfe7f7f7c0

java/app_test.go

@@ -147,7 +147,7 @@ func TestAndroidAppSet(t *testing.T) {
 			name: "foo",
 			set: "prebuilts/apks/app.apks",
 			prerelease: true,
-        }`)
+		}`)
 	module := ctx.ModuleForTests("foo", "android_common")
 	const packedSplitApks = "foo.zip"
 	params := module.Output(packedSplitApks)
@@ -157,6 +157,9 @@ func TestAndroidAppSet(t *testing.T) {
 	if s := params.Args["allow-prereleased"]; s != "true" {
 		t.Errorf("wrong allow-prereleased value: '%s', expected 'true'", s)
 	}
+	if s := params.Args["partition"]; s != "system" {
+		t.Errorf("wrong partition value: '%s', expected 'system'", s)
+	}
 	mkEntries := android.AndroidMkEntriesForTest(t, config, "", module.Module())[0]
 	actualMaster := mkEntries.EntryMap["LOCAL_APK_SET_MASTER_FILE"]
 	expectedMaster := []string{"foo.apk"}