Add a feature to get the last UpdateAttempt ErrorCode from update_engine

For autotest, update_engine test failures are always hard to debug,
since the error message is not clear. Add a new flag 'last_attempt_error'
to get the last UpdateAttempt ErrorCode from update_engine.

Bug:25598547
Test:emerge-peppy update_engine
     emerge-peppy update_engine_client
     cros flash a test image to DUT.
     (on the DUT):update_engine_client --last_attempt_error
     Compare the results with the update_engine logs, matched.

Change-Id: Id12681097ed30b0826cad68809f17f934a07e5b2
diff --git a/update_engine.gyp b/update_engine.gyp
index ab20243..7da34fb 100644
--- a/update_engine.gyp
+++ b/update_engine.gyp
@@ -334,7 +334,8 @@
       ],
       'sources': [
         'update_engine_client.cc',
-      ],
+        'common/error_code_utils.cc',
+     ],
     },
     # server-side code. This is used for delta_generator and unittests but not
     # for any client code.