Ensure we log the mode during reboot

default toString will print nothing for REBOOT_FULL

Test: unit tests
Bug: None
Change-Id: I30d9131c7b273769e1cfc77a929bee33b7b74058
diff --git a/src/com/android/tradefed/device/NativeDevice.java b/src/com/android/tradefed/device/NativeDevice.java
index 949bd24..e9a4359 100644
--- a/src/com/android/tradefed/device/NativeDevice.java
+++ b/src/com/android/tradefed/device/NativeDevice.java
@@ -3163,11 +3163,11 @@
                 return;
             }
             if (reason == null) {
-                CLog.i("Rebooting device %s mode: %s", getSerialNumber(), rebootMode);
+                CLog.i("Rebooting device %s mode: %s", getSerialNumber(), rebootMode.name());
             } else {
                 CLog.i(
                         "Rebooting device %s mode: %s reason: %s",
-                        getSerialNumber(), rebootMode, reason);
+                        getSerialNumber(), rebootMode.name(), reason);
             }
             doAdbReboot(rebootMode, reason);
             // Check if device shows as unavailable (as expected after reboot).