update_engine: Make dd less verbose.

update_engine unit tests use the "dd" command for setting up some test
cases. By default, dd print the status of the operation on success.

This patch removes the status message reducing the unnecessary logs.

BUG=None
TEST=`FEATURES=test emerge-link update_engine`

Change-Id: I6dbb7029a8dce9acf1309da1844af558a2bdab56
Reviewed-on: https://chromium-review.googlesource.com/259190
Reviewed-by: Don Garrett <[email protected]>
Commit-Queue: Alex Deymo <[email protected]>
Trybot-Ready: Alex Deymo <[email protected]>
Tested-by: Alex Deymo <[email protected]>
diff --git a/postinstall_runner_action_unittest.cc b/postinstall_runner_action_unittest.cc
index fc61f4e..0460c6c 100644
--- a/postinstall_runner_action_unittest.cc
+++ b/postinstall_runner_action_unittest.cc
@@ -129,7 +129,8 @@
 
   // Create a 10MiB sparse file to be used as image; format it as ext2.
   ASSERT_EQ(0, System(
-          "dd if=/dev/zero of=image.dat seek=10485759 bs=1 count=1"));
+          "dd if=/dev/zero of=image.dat seek=10485759 bs=1 count=1 "
+          "status=none"));
   ASSERT_EQ(0, System("mkfs.ext2 -F image.dat"));
 
   // Create a uniquely named image mount point, mount the image.