[REFACTOR] DynamicPartitionControl: Add GetSuperPartitionName

fs_mgr_get_super_partition_name() should be mocked because
it is an external dependency to libfs_mgr.

In tests, deliberately make GetSuperDevice() to return "fake_super"
instead of "super" to make sure it is mocked properly.

Test: run unittests
Test: manually apply OTA

Change-Id: I0f05d99bf168b6e658052b4bd67dc1e82ab36471
diff --git a/dynamic_partition_control_android.h b/dynamic_partition_control_android.h
index dc152cc..062a2d1 100644
--- a/dynamic_partition_control_android.h
+++ b/dynamic_partition_control_android.h
@@ -48,6 +48,7 @@
                                   const BootControlInterface::PartitionMetadata&
                                       partition_metadata) override;
   bool GetDeviceDir(std::string* path) override;
+  std::string GetSuperPartitionName(uint32_t slot) override;
 
  protected:
   // These functions are exposed for testing.