Consolidate the codes that handle reboot/shutdown.

Test: Choose `Reboot system now`, `Power off`, `Reboot to bootloader`
      from recovery UI respectively.
Test: `adb reboot recovery` while under sideload mode.
Change-Id: I0f3d55b80b472178ea4f6970b29cd9df0778b639
diff --git a/updater/install.cpp b/updater/install.cpp
index 20a204a..8eba64f 100644
--- a/updater/install.cpp
+++ b/updater/install.cpp
@@ -778,7 +778,7 @@
     return StringValue("");
   }
 
-  reboot("reboot," + property);
+  Reboot(property);
 
   sleep(5);
   return ErrorAbort(state, kRebootFailure, "%s() failed to reboot", name);