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_solaris_test.go

@@ -11,6 +11,7 @@ import (
 	"fmt"
 	"os"
 	"os/exec"
+	"path/filepath"
 	"runtime"
 	"strings"
 	"testing"
@@ -83,12 +84,12 @@ func TestSysconf(t *testing.T) {
 // Event Ports
 
 func TestBasicEventPort(t *testing.T) {
-	tmpfile, err := os.CreateTemp("", "eventport")
+	tmpfile, err := os.Create(filepath.Join(t.TempDir(), "eventport"))
 	if err != nil {
-		t.Fatalf("unable to create a tempfile: %v", err)
+		t.Fatal(err)
 	}
+	defer tmpfile.Close()
 	path := tmpfile.Name()
-	defer os.Remove(path)
 
 	stat, err := os.Stat(path)
 	if err != nil {