Map all partitions before calling FinishUpdate for VAB as well

In virtual AB updates, all partitions must be mapped before calling
FinishUpdate. (same requirement as VABC).

Test: install VAB update w/o slot switch, then perform slot switch
Bug: 393082101
Change-Id: Iec7965b2d1a75b8a61507d75c83c733bfac38ce4
diff --git a/common/fake_boot_control.h b/common/fake_boot_control.h
index 8a68501..82d4827 100644
--- a/common/fake_boot_control.h
+++ b/common/fake_boot_control.h
@@ -40,6 +40,11 @@
     dynamic_partition_control_.reset(new DynamicPartitionControlStub());
   }
 
+  void SetDynamicPartitionControl(
+      std::unique_ptr<DynamicPartitionControlInterface> dynamic_control) {
+    dynamic_partition_control_ = std::move(dynamic_control);
+  }
+
   // BootControlInterface overrides.
   unsigned int GetNumSlots() const override { return num_slots_; }
   BootControlInterface::Slot GetCurrentSlot() const override {