update_engine: update error log

Current error log will just print the error code number without actually
telling us what the error is. Current wording also suggests the op is
printed rather than the errorcode.

Test: th
Change-Id: Ia9ae6435df37d726f615cd5e63770522af88b546
diff --git a/payload_consumer/delta_performer.cc b/payload_consumer/delta_performer.cc
index fe581b6..519ec71 100644
--- a/payload_consumer/delta_performer.cc
+++ b/payload_consumer/delta_performer.cc
@@ -503,7 +503,9 @@
     if (!CanPerformInstallOperation(op))
       return true;
     if (!ProcessOperation(&op, error)) {
-      LOG(ERROR) << "unable to process operation: " << *error;
+      LOG(ERROR) << "unable to process operation: "
+                 << InstallOperationTypeName(op.type())
+                 << " Error: " << utils::ErrorCodeToString(*error);
       return false;
     }