recovery: fix use of init reboot method

We need to set the system property to "reboot,", not an empty string.

Bug: 10605007
Change-Id: I776e0d273764cf254651ab2b25c2743395b990e0

recovery.cpp

@@ -1062,6 +1062,6 @@ main(int argc, char **argv) {
     // Otherwise, get ready to boot the main system...
     finish_recovery(send_intent);
     ui->Print("Rebooting...\n");
-    property_set(ANDROID_RB_PROPERTY, "");
+    property_set(ANDROID_RB_PROPERTY, "reboot,");
     return EXIT_SUCCESS;
 }