Simplify Utsname string conversion

Use Utsname from golang.org/x/sys/unix which contains byte array
instead of int8/uint8 array members. This allows to simplify the string
conversions of these members and the marshal.FromUtsname functions are
no longer needed.

probe/host/system_linux_test.go

@@ -2,10 +2,11 @@ package host_test
 
 import (
 	"fmt"
-	"syscall"
 	"testing"
 
 	"github.com/weaveworks/scope/probe/host"
+
+	"golang.org/x/sys/unix"
 )
 
 func TestUname(t *testing.T) {
@@ -16,9 +17,9 @@ func TestUname(t *testing.T) {
 		release = "rls"
 		version = "ver"
 	)
-	host.Uname = func(uts *syscall.Utsname) error {
-		uts.Release = string2c(release)
-		uts.Version = string2c(version)
+	host.Uname = func(uts *unix.Utsname) error {
+		copy(uts.Release[:], []byte(release))
+		copy(uts.Version[:], []byte(version))
 		return nil
 	}
 
@@ -31,11 +32,3 @@ func TestUname(t *testing.T) {
 		t.Errorf("want %q, have %q", want, have)
 	}
 }
-
-func string2c(s string) [65]int8 {
-	var result [65]int8
-	for i, c := range s {
-		result[i] = int8(c)
-	}
-	return result
-}