AU: shift to use new TMPDIR-enabled temp file

The main change here is that delta generator will now create all
temporary files in TMPDIR, if set. Other than that, we're converting all
other temporary file/directory creation to use the new functions.

- All temps of the form "/tmp/foo" are converted to "foo": this
  preserves the behavior in the default case (where TMPDIR is not set),
  yet will do the right thing if run with a different TMPDIR.

- A few other cases (for example, temp file created relative to the
  current working directory) will now be created in TMPDIR or /tmp.
  These are all in unit tests and the transition makes sense anyway.

Note that two temp file/directory creation calls in actual UE code were
using "/tmp/..." and were not changed. This will ensure that they are
resilient to TMPDIR changes and will always be allocated in the same
(hard-coded) location.

BUG=chromium:253622
TEST=Unit tests.

Change-Id: Ia1208963a0e2fcd43b8d6f92bb3d1b7459e930a2
Reviewed-on: https://chromium-review.googlesource.com/182247
Tested-by: Gilad Arnold <garnold@chromium.org>
Reviewed-by: Don Garrett <dgarrett@chromium.org>
Commit-Queue: Gilad Arnold <garnold@chromium.org>
diff --git a/full_update_generator_unittest.cc b/full_update_generator_unittest.cc
index 16aa568..c04773e 100644
--- a/full_update_generator_unittest.cc
+++ b/full_update_generator_unittest.cc
@@ -33,14 +33,14 @@
   off_t new_rootfs_size = new_root.size() - 2 * 1024 * 1024;
 
   string new_root_path;
-  EXPECT_TRUE(utils::MakeTempFile("/tmp/NewFullUpdateTest_R.XXXXXX",
+  EXPECT_TRUE(utils::MakeTempFile("NewFullUpdateTest_R.XXXXXX",
                                   &new_root_path,
                                   NULL));
   ScopedPathUnlinker new_root_path_unlinker(new_root_path);
   EXPECT_TRUE(WriteFileVector(new_root_path, new_root));
 
   string new_kern_path;
-  EXPECT_TRUE(utils::MakeTempFile("/tmp/NewFullUpdateTest_K.XXXXXX",
+  EXPECT_TRUE(utils::MakeTempFile("NewFullUpdateTest_K.XXXXXX",
                                   &new_kern_path,
                                   NULL));
   ScopedPathUnlinker new_kern_path_unlinker(new_kern_path);
@@ -48,7 +48,7 @@
 
   string out_blobs_path;
   int out_blobs_fd;
-  EXPECT_TRUE(utils::MakeTempFile("/tmp/NewFullUpdateTest_D.XXXXXX",
+  EXPECT_TRUE(utils::MakeTempFile("NewFullUpdateTest_D.XXXXXX",
                                   &out_blobs_path,
                                   &out_blobs_fd));
   ScopedPathUnlinker out_blobs_path_unlinker(out_blobs_path);