Add override_module.

This new module type replaces the inherit-package function in make by
allowing developers to override the name, the certificate, and the
manifest package name of an android_app module.

Bug: 122957760
Fixes: 123640028
Test: app_test.go + BrowserGoogle
Change-Id: Iefe447e7078b25039233221361ef95c83a29973a

apex/apex.go

@@ -534,7 +534,7 @@ func (a *apexBundle) DepsMutator(ctx android.BottomUpMutatorContext) {
 func (a *apexBundle) getCertString(ctx android.BaseContext) string {
 	certificate, overridden := ctx.DeviceConfig().OverrideCertificateFor(ctx.ModuleName())
 	if overridden {
-		return ":" + certificate
+		return certificate
 	}
 	return String(a.properties.Certificate)
 }