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/utils_unittest.cc b/utils_unittest.cc
index fa97f55..a9ce287 100644
--- a/utils_unittest.cc
+++ b/utils_unittest.cc
@@ -2,9 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include <errno.h>
 #include <sys/stat.h>
 #include <sys/types.h>
-#include <errno.h>
 
 #include <map>
 #include <string>