Provide better sethostname error message

This tries to add a marginally better error message including the hostname when the syscall fails. 

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>
yes! its the best :) it quotes them

On Fri, Nov 14, 2014 at 6:03 PM, Mrunal Patel <notifications@github.com>
wrote:

> In namespaces/init.go:
>
> > @@ -100,7 +100,7 @@ func Init(container *libcontainer.Config, uncleanRootfs, consolePath string, pip
> >
> >  	if container.Hostname != "" {
> >  		if err := syscall.Sethostname([]byte(container.Hostname)); err != nil {
> > -			return fmt.Errorf("sethostname %s", err)
> > +			return fmt.Errorf("unable to sethostname %q: %s", container.Hostname, err)
>
> %q works with strings?
>
> —
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> <https://github.com/docker/libcontainer/pull/268/files#r20398661>.
>