init: add reboot_on_failure service option

This replaces the recently added `exec_reboot_on_failure` builtin, since
it'll be cleaner to extend service definitions than extending `exec`.
This is in line with what we decided when adding `exec_start` instead
of extending `exec` to add parameters for priority.

Test: `exec_start` a service with a reboot_on_failure option and watch
      the system reboot appropriately when the service is not found and when
      the service terminates with a non-zero exit code.

Change-Id: I332bf9839fa94840d159a810c4a6ba2522189d0b
diff --git a/init/init.h b/init/init.h
index 8ac52e2..61fb110 100644
--- a/init/init.h
+++ b/init/init.h
@@ -31,6 +31,8 @@
 Parser CreateParser(ActionManager& action_manager, ServiceList& service_list);
 Parser CreateServiceOnlyParser(ServiceList& service_list);
 
+void EnterShutdown(const std::string& command);
+
 bool start_waiting_for_property(const char *name, const char *value);
 
 void DumpState();