Use libsnapshot stub classes

... to avoid crashes in update_engine. The stub classes
does nothing but return a failure for all function
calls, and act as if Virtual A/B is not enabled.

Fixes: 148956645
Test: update_engine_unittests
Change-Id: I48206958aba8d9a71cc7cf49f6b9d5d4f1c8735d
diff --git a/dynamic_partition_control_android.h b/dynamic_partition_control_android.h
index 8ad7593..4918ea6 100644
--- a/dynamic_partition_control_android.h
+++ b/dynamic_partition_control_android.h
@@ -258,7 +258,7 @@
   std::set<std::string> mapped_devices_;
   const FeatureFlag dynamic_partitions_;
   const FeatureFlag virtual_ab_;
-  std::unique_ptr<android::snapshot::SnapshotManager> snapshot_;
+  std::unique_ptr<android::snapshot::ISnapshotManager> snapshot_;
   std::unique_ptr<android::snapshot::AutoDevice> metadata_device_;
   bool target_supports_snapshot_ = false;
   // Whether the target partitions should be loaded as dynamic partitions. Set