update_engine: Remove dependency on libupdate_engine from the client.

The update_engine_client is a very small DBus client that only
depends on a single utils:: function from the update_engine daemon
codebase. Because of this, it was forced to be linked against many
libraries that it didn't use.

This patch factors out this glib helper function to a new
glib_utils.{cc,h} file and includes only that in the
update_engine_client binary.

BUG=chromium:396440
TEST=FEATURES=test emerge-link update_engine

Change-Id: Icf8d8b3c6ebd22cdb39e6674fb3d9071071ec941
Reviewed-on: https://chromium-review.googlesource.com/209472
Reviewed-by: David Zeuthen <zeuthen@chromium.org>
Tested-by: Alex Deymo <deymo@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>
diff --git a/filesystem_copier_action.cc b/filesystem_copier_action.cc
index 23d3b0e..efd454d 100644
--- a/filesystem_copier_action.cc
+++ b/filesystem_copier_action.cc
@@ -20,6 +20,7 @@
 #include <gio/gunixoutputstream.h>
 #include <glib.h>
 
+#include "update_engine/glib_utils.h"
 #include "update_engine/hardware_interface.h"
 #include "update_engine/subprocess.h"
 #include "update_engine/system_state.h"