[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_test_utils.h b/dynamic_partition_test_utils.h
index 2cfdff5..574d30e 100644
--- a/dynamic_partition_test_utils.h
+++ b/dynamic_partition_test_utils.h
@@ -48,6 +48,7 @@
 constexpr const char* kFakeDmDevicePath = "/fake/dm/dev/path/";
 constexpr const uint32_t kFakeMetadataSize = 65536;
 constexpr const char* kDefaultGroup = "foo";
+constexpr const char* kFakeSuper = "fake_super";
 
 // A map describing the size of each partition.
 // "{name, size}"
@@ -121,11 +122,6 @@
   return kFakeDmDevicePath + name;
 }
 
-// TODO(elsk): fs_mgr_get_super_partition_name should be mocked.
-inline std::string GetSuperDevice(uint32_t slot) {
-  return GetDevice(fs_mgr_get_super_partition_name(slot));
-}
-
 // To support legacy tests, auto-convert {name_a: size} map to
 // PartitionMetadata.
 inline PartitionMetadata PartitionSuffixSizesToMetadata(