Add test to ReadFstabFromDt in the VtsGsiBootTest

This test is added to address the init behavior in
first_stage_mount in order to make sure /metadata can be early
mounted on devices that still use dt-fstab.

Bug: 138449350
Test: vts-tradefed> run vts -m VtsGsiBootTest
Change-Id: If1c5f037f7850f6237e60f3e0cb19f429a3abebd
diff --git a/tests/boot_tests.cpp b/tests/boot_tests.cpp
index a8b623d..a00e798 100644
--- a/tests/boot_tests.cpp
+++ b/tests/boot_tests.cpp
@@ -29,11 +29,15 @@
 
 TEST(MetadataPartition, FirstStageMount) {
     Fstab fstab;
-    ASSERT_TRUE(ReadDefaultFstab(&fstab));
-
-    auto entry = GetEntryForMountPoint(&fstab, "/metadata");
-    ASSERT_NE(entry, nullptr);
-    EXPECT_TRUE(entry->fs_mgr_flags.first_stage_mount);
+    if (ReadFstabFromDt(&fstab)) {
+        auto entry = GetEntryForMountPoint(&fstab, "/metadata");
+        ASSERT_NE(entry, nullptr);
+    } else {
+        ASSERT_TRUE(ReadDefaultFstab(&fstab));
+        auto entry = GetEntryForMountPoint(&fstab, "/metadata");
+        ASSERT_NE(entry, nullptr);
+        EXPECT_TRUE(entry->fs_mgr_flags.first_stage_mount);
+    }
 }
 
 TEST(MetadataPartition, MinimumSize) {