fix failing garage mode test

- Populate Handler

bug: 27112153
Change-Id: I3802268271e6f3e145b731bfcdad5a04e8cbb90c
diff --git a/service/src/com/android/car/CarPowerManagementService.java b/service/src/com/android/car/CarPowerManagementService.java
index ef49e47..3220bea 100644
--- a/service/src/com/android/car/CarPowerManagementService.java
+++ b/service/src/com/android/car/CarPowerManagementService.java
@@ -167,7 +167,7 @@
         mHal = null;
         mSystemInterface = null;
         mHandlerThread = null;
-        mHandler = null;
+        mHandler = new PowerHandler(Looper.getMainLooper());
     }
 
     @Override