Android: Print the error code string from the client.

The update_engine_client needs to translate the numeric ErrorCode to a
string name that can be printed on the output. This patch moves the
ErrorCodeToString() function to a new error_code_utils.{h,cc} pair of
files so it can be included easily from the client binary and uses it
in the Android update_engine_client.

Bug: 25631767
Bug: 25598547
TEST=`update_engine_client --update` prints the error message in a non-Brillo device.

Change-Id: Ib40813924ec676f3e703412de90d389b2596177e
diff --git a/payload_state.cc b/payload_state.cc
index 38a36f9..4b5b5fd 100644
--- a/payload_state.cc
+++ b/payload_state.cc
@@ -27,6 +27,7 @@
 
 #include "update_engine/common/clock.h"
 #include "update_engine/common/constants.h"
+#include "update_engine/common/error_code_utils.h"
 #include "update_engine/common/hardware_interface.h"
 #include "update_engine/common/prefs.h"
 #include "update_engine/common/utils.h"
@@ -242,7 +243,7 @@
 void PayloadState::UpdateFailed(ErrorCode error) {
   ErrorCode base_error = utils::GetBaseErrorCode(error);
   LOG(INFO) << "Updating payload state for error code: " << base_error
-            << " (" << utils::CodeToString(base_error) << ")";
+            << " (" << utils::ErrorCodeToString(base_error) << ")";
 
   if (candidate_urls_.size() == 0) {
     // This means we got this error even before we got a valid Omaha response