Use crypto/rand.Read, not crypto.Reader.Read

The current code accidentally ignores partial reads, since it doesn't
check the return value of (io.Reader).Read.

What we actually want is io.ReadFull(rand.Reader, buf), which is
conveniently provided by rand.Read(buf).

Signed-off-by: edef <edef@edef.eu>

pkg/testutils/netns_linux.go

@@ -53,7 +53,7 @@ func NewNS() (ns.NetNS, error) {
 	nsRunDir := getNsRunDir()
 
 	b := make([]byte, 16)
-	_, err := rand.Reader.Read(b)
+	_, err := rand.Read(b)
 	if err != nil {
 		return nil, fmt.Errorf("failed to generate random netns name: %v", err)
 	}