unix: remove usage of ioutil.TempFile in tests

Mostly change that to os.Create(filepath.Join(t.TempDir(), "filename"))
so that the cleanup is done automatically (and, because this is a new
directory, we do not need to have a "create unique temp file name"
logic).

While at it, fix some log/error messages -- if an error is coming from
e.g. os package, it is already wrapped, so there's no need to add more
context.

Change-Id: I62f13679f256b94095be5ca1e77a3fa302f01b97
Reviewed-on: https://go-review.googlesource.com/c/sys/+/526298
Reviewed-by: Heschi Kreinick <heschi@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Run-TryBot: Kirill Kolyshkin <kolyshkin@gmail.com>

unix/syscall_linux_test.go

@@ -688,11 +688,10 @@ func TestFaccessat(t *testing.T) {
 }
 
 func TestSyncFileRange(t *testing.T) {
-	file, err := ioutil.TempFile("", "TestSyncFileRange")
+	file, err := os.Create(filepath.Join(t.TempDir(), t.Name()))
 	if err != nil {
 		t.Fatal(err)
 	}
-	defer os.Remove(file.Name())
 	defer file.Close()
 
 	err = unix.SyncFileRange(int(file.Fd()), 0, 0, 0)
@@ -1024,12 +1023,12 @@ func TestOpenat2(t *testing.T) {
 }
 
 func TestIoctlFileDedupeRange(t *testing.T) {
-	f1, err := ioutil.TempFile("", t.Name())
+	dir := t.TempDir()
+	f1, err := os.Create(filepath.Join(dir, "f1"))
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer f1.Close()
-	defer os.Remove(f1.Name())
 
 	// Test deduplication with two blocks of zeros
 	data := make([]byte, 4096)
@@ -1041,12 +1040,11 @@ func TestIoctlFileDedupeRange(t *testing.T) {
 		}
 	}
 
-	f2, err := ioutil.TempFile("", t.Name())
+	f2, err := os.Create(filepath.Join(dir, "f2"))
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer f2.Close()
-	defer os.Remove(f2.Name())
 
 	for i := 0; i < 2; i += 1 {
 		// Make the 2nd block different