AU: clean up logs

- don't log for each operation when doing a delta update (there are
  thousands)
- Fix subprocess to only log if there is output
- Fix subprocess to say 'subprocess' rather than 'postinst', since the
  sub process is not always postinst :)

BUG=5928
TEST=unit tests

Review URL: http://codereview.chromium.org/3119031
diff --git a/delta_performer.cc b/delta_performer.cc
index 8cf0226..04273f3 100644
--- a/delta_performer.cc
+++ b/delta_performer.cc
@@ -193,8 +193,12 @@
             next_operation_num_ - manifest_.install_operations_size());
     if (!CanPerformInstallOperation(op))
       break;
-    LOG(INFO) << "Performing operation " << next_operation_num_ << "/"
-              << total_operations;
+    // Log every thousandth operation, and also the first and last ones
+    if ((next_operation_num_ % 1000 == 0) ||
+        (next_operation_num_ + 1 == total_operations)) {
+      LOG(INFO) << "Performing operation " << (next_operation_num_ + 1) << "/"
+                << total_operations;
+    }
     bool is_kernel_partition =
         (next_operation_num_ >= manifest_.install_operations_size());
     if (op.type() == DeltaArchiveManifest_InstallOperation_Type_REPLACE ||
diff --git a/subprocess.cc b/subprocess.cc
index c319a22..99605dd 100755
--- a/subprocess.cc
+++ b/subprocess.cc
@@ -139,10 +139,10 @@
   FreeArgv(argv.get());
   if (err)
     LOG(INFO) << "err is: " << err->code << ", " << err->message;
-  if (child_stdout)
-    LOG(INFO) << "Postinst stdout:" << child_stdout;
-  if (child_stderr)
-    LOG(INFO) << "Postinst stderr:" << child_stderr;
+  if (child_stdout && strlen(child_stdout))
+    LOG(INFO) << "Subprocess stdout:" << child_stdout;
+  if (child_stderr && strlen(child_stderr))
+    LOG(INFO) << "Subprocess stderr:" << child_stderr;
   return success;
 }