AU: Changes for deltas on traditional bios machines.

BUG=None
TEST=Attached unittests/tested on image

- Fix uninitialized variable err in action processor unittest

- Let Omaha dictate if an update is a delta or full update

- Bug fix in delta generator for differently-sized images

- More logging when applying delta updates

- Fix infinite loop in http fetcher unittest

- log each HTTP connection to know when a dropped connection is
  reestablished.

- Detect when speed goes below a threshold and reestablish HTTP
  connection (currently < 10bytes/sec for 90 contiguous seconds).

- Fix stack overflow in libcurl http fetcher.

- optimize out a lot of needless CPU usage in libcurl http fetcher
  (turns out adding a glib main loop source uses a lot of CPU).

- subprocess: pass PATH, log stdout/stderr

- postinstall runner: support for ext3 and ext4 target filesystems.

Review URL: http://codereview.chromium.org/2805027
diff --git a/delta_performer_unittest.cc b/delta_performer_unittest.cc
index 89999eb..fe12b9b 100755
--- a/delta_performer_unittest.cc
+++ b/delta_performer_unittest.cc
@@ -74,8 +74,8 @@
 
 void CompareFilesByBlock(const string& a_file, const string& b_file) {
   vector<char> a_data, b_data;
-  EXPECT_TRUE(utils::ReadFile(a_file, &a_data));
-  EXPECT_TRUE(utils::ReadFile(b_file, &b_data));
+  EXPECT_TRUE(utils::ReadFile(a_file, &a_data)) << "file failed: " << a_file;
+  EXPECT_TRUE(utils::ReadFile(b_file, &b_data)) << "file failed: " << b_file;
 
   EXPECT_EQ(a_data.size(), b_data.size());
   size_t kBlockSize = 4096;