On-device signing: Add TEST_MAPPING.

On-device signing end-to-end test now passes on cuttlefish, too.

Bug: 167516462
Change-Id: I327326d86d34233ab8921e9313516717102b899e
Test: atest
diff --git a/ondevice-signing/TEST_MAPPING b/ondevice-signing/TEST_MAPPING
new file mode 100644
index 0000000..03b9b95
--- /dev/null
+++ b/ondevice-signing/TEST_MAPPING
@@ -0,0 +1,7 @@
+{
+  "presubmit": [
+    {
+      "name": "odsign_e2e_tests"
+    }
+  ]
+}