Move snapuserd_test to postsubmit

Bug: 338329603
Test: Build
Change-Id: Ibee6be732078ea7e11fe7348772837b9b2699fbf
Signed-off-by: Akilesh Kailash <akailash@google.com>
diff --git a/fs_mgr/TEST_MAPPING b/fs_mgr/TEST_MAPPING
index 192232d..13af1e2 100644
--- a/fs_mgr/TEST_MAPPING
+++ b/fs_mgr/TEST_MAPPING
@@ -27,7 +27,9 @@
     },
     {
       "name": "cow_api_test"
-    },
+    }
+  ],
+  "postsubmit": [
     {
       "name": "snapuserd_test"
     }