update_engine: Sort headers alphabetically (build/include_alpha)

We are going to enable build/include_alpha linter warning soon,
so in preparation for this, fixed the warnings in update_engine.

BUG=None
TEST=cpplint.py --filter=-build/include_order,+build/include_alpha update_engine/*
CQ-DEPEND=CL:209472

Change-Id: I261ea04681599a68ec7cb899f2f881cbe228ff7b
Reviewed-on: https://chromium-review.googlesource.com/209631
Reviewed-by: Alex Deymo <deymo@chromium.org>
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>
diff --git a/main.cc b/main.cc
index 83b9a4b..c7d724b 100644
--- a/main.cc
+++ b/main.cc
@@ -26,11 +26,10 @@
 #include "update_engine/terminator.h"
 #include "update_engine/update_attempter.h"
 #include "update_engine/update_check_scheduler.h"
-#include "update_engine/utils.h"
-
 extern "C" {
 #include "update_engine/update_engine.dbusserver.h"
 }
+#include "update_engine/utils.h"
 
 DEFINE_bool(logtostderr, false,
             "Write logs to stderr instead of to a file in log_dir.");