Fixes to utility / unit test related code.

* Eliminated bugs related to reading content from pipes/files, including
  general cleanup/refactoring of these code pieces and API.

* Eliminated bugs related binding/unbinding of loopback devices, which
  are used in unit testing.

BUG=chromium-os:31082
TEST=Builds and runs unit tests

CQ-DEPEND=Ib7b3552e98ca40b6141688e2dea5a1407db12b2a

Change-Id: Ifaab8697602a35ce7d7fb9384fdcb1ca64b72515
Reviewed-on: https://gerrit.chromium.org/gerrit/27911
Reviewed-by: Don Garrett <dgarrett@chromium.org>
Tested-by: Gilad Arnold <garnold@chromium.org>
Commit-Ready: Gilad Arnold <garnold@chromium.org>
diff --git a/omaha_response_handler_action_unittest.cc b/omaha_response_handler_action_unittest.cc
index 87fa1e8..9da48a6 100644
--- a/omaha_response_handler_action_unittest.cc
+++ b/omaha_response_handler_action_unittest.cc
@@ -107,7 +107,7 @@
     EXPECT_EQ(in.hash, install_plan.download_hash);
     EXPECT_EQ("/dev/sda5", install_plan.install_path);
     string deadline;
-    EXPECT_TRUE(utils::ReadFileToString(
+    EXPECT_TRUE(utils::ReadFile(
         OmahaResponseHandlerAction::kDeadlineFile,
         &deadline));
     EXPECT_EQ("20101020", deadline);
@@ -133,7 +133,7 @@
     EXPECT_EQ(in.hash, install_plan.download_hash);
     EXPECT_EQ("/dev/sda3", install_plan.install_path);
     string deadline;
-    EXPECT_TRUE(utils::ReadFileToString(
+    EXPECT_TRUE(utils::ReadFile(
         OmahaResponseHandlerAction::kDeadlineFile,
         &deadline) && deadline.empty());
   }
@@ -154,7 +154,7 @@
     EXPECT_EQ(in.hash, install_plan.download_hash);
     EXPECT_EQ("/dev/sda5", install_plan.install_path);
     string deadline;
-    EXPECT_TRUE(utils::ReadFileToString(
+    EXPECT_TRUE(utils::ReadFile(
         OmahaResponseHandlerAction::kDeadlineFile,
         &deadline));
     EXPECT_EQ("some-deadline", deadline);