Disable post-install on major version 1 payloads in Brillo.

Brillo uses payload major version 2, which provides a specification of
what post-install commands to run. This patch disables post-install for
major version 1 payloads on Brillo, which allows backwards
compatibility when updating Brillo builds with old payloads.

Bug: 23186405
Test: Updated a dragonboard running update_engine from init using a payload v1.

Change-Id: Ic4a8259eedba30d534c008debe5b75a693db1cf2
diff --git a/delta_performer.cc b/delta_performer.cc
index 4d08c82..ef03cb7 100644
--- a/delta_performer.cc
+++ b/delta_performer.cc
@@ -702,7 +702,14 @@
     LOG(INFO) << "Converting update information from old format.";
     PartitionUpdate root_part;
     root_part.set_partition_name(kLegacyPartitionNameRoot);
+#ifdef __ANDROID__
+    LOG(WARNING) << "Legacy payload major version provided to an Android "
+                    "build. Assuming no post-install. Please use major version "
+                    "2 or newer.";
+    root_part.set_run_postinstall(false);
+#else
     root_part.set_run_postinstall(true);
+#endif  // __ANDROID__
     if (manifest_.has_old_rootfs_info()) {
       *root_part.mutable_old_partition_info() = manifest_.old_rootfs_info();
       manifest_.clear_old_rootfs_info();