[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_unittest.cc b/dynamic_partition_control_android_unittest.cc
index 2fa0f16..5b3dfe3 100644
--- a/dynamic_partition_control_android_unittest.cc
+++ b/dynamic_partition_control_android_unittest.cc
@@ -50,6 +50,9 @@
           *path = kFakeDevicePath;
           return true;
         }));
+
+    ON_CALL(dynamicControl(), GetSuperPartitionName(_))
+        .WillByDefault(Return(kFakeSuper));
   }
 
   // Return the mocked DynamicPartitionControlInterface.
@@ -57,6 +60,10 @@
     return static_cast<NiceMock<MockDynamicPartitionControlAndroid>&>(*module_);
   }
 
+  std::string GetSuperDevice(uint32_t slot) {
+    return GetDevice(dynamicControl().GetSuperPartitionName(slot));
+  }
+
   uint32_t source() { return slots_.source; }
   uint32_t target() { return slots_.target; }