Turn on UserspaceRebootHostTest in post-submit phase

Bug: 151704489
Test: m
Change-Id: I9ec7c64c71e224087a47494b6d8f2553cfc3ae14
diff --git a/hostsidetests/userspacereboot/TEST_MAPPING b/hostsidetests/userspacereboot/TEST_MAPPING
index d0a1adb..e066051 100644
--- a/hostsidetests/userspacereboot/TEST_MAPPING
+++ b/hostsidetests/userspacereboot/TEST_MAPPING
@@ -4,5 +4,10 @@
       "name": "CtsUserspaceRebootHostSideTestCases",
       "keywords": ["primary-device"]
     }
+  ],
+  "postsubmit": [
+    {
+      "name": "CtsUserspaceRebootHostSideTestCases"
+    }
   ]
 }