unix: convert Utsname members from {u,}int8 array to byte array

In order to make conversion to string easier, change the Utsname
members from int8 array to byte array.

Also add a test on Linux for Uname and the string conversion of the
Utsname members.

Fixes golang/go#20753

Change-Id: Iec793dfb4a6dd8f3523cf0b6284a6162074f2e9e
Reviewed-on: https://go-review.googlesource.com/74331
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/unix/ztypes_linux_mipsle.go b/unix/ztypes_linux_mipsle.go
index 75ee05a..b6c2d32 100644
--- a/unix/ztypes_linux_mipsle.go
+++ b/unix/ztypes_linux_mipsle.go
@@ -614,12 +614,12 @@
 }
 
 type Utsname struct {
-	Sysname    [65]int8
-	Nodename   [65]int8
-	Release    [65]int8
-	Version    [65]int8
-	Machine    [65]int8
-	Domainname [65]int8
+	Sysname    [65]byte
+	Nodename   [65]byte
+	Release    [65]byte
+	Version    [65]byte
+	Machine    [65]byte
+	Domainname [65]byte
 }
 
 type Ustat_t struct {