Support IsDeltaPayload per <package>.

Mixed full and delta payloads are now supported for multi-payload.

Bug: 36252799
Test: update_engine_unittests
Change-Id: Ic519f8399579c714a65ba9f9f948a389fcc249ed
(cherry picked from commit 4928112f8635f7a5b583171640aee2bda690ba34)
diff --git a/update_attempter_android.cc b/update_attempter_android.cc
index 09549f8..286ed65 100644
--- a/update_attempter_android.cc
+++ b/update_attempter_android.cc
@@ -161,6 +161,8 @@
                             &payload.metadata_size)) {
     payload.metadata_size = 0;
   }
+  // The |payload.type| is not used anymore since minor_version 3.
+  payload.type = InstallPayloadType::kUnknown;
   install_plan_.payloads.push_back(payload);
 
   // The |public_key_rsa| key would override the public key stored on disk.
@@ -177,9 +179,6 @@
       LOG(WARNING) << "Unable to save the update check response hash.";
     }
   }
-  // The |payload_type| is not used anymore since minor_version 3.
-  install_plan_.payload_type = InstallPayloadType::kUnknown;
-
   install_plan_.source_slot = boot_control_->GetCurrentSlot();
   install_plan_.target_slot = install_plan_.source_slot == 0 ? 1 : 0;