Fix multiple attach test.

This increases the window between the sleep and the attach; this allows the `docker run` to finish processing even on the slowest systems (like my VM!).

I've run the test about 20 times without a single issue. in `#docci-test` on freenode you can see this test failing about 50% of the time at the moment.
fixed
> On Aug 22, 2014, at 3:54 AM, Alexandr Morozov <notifications@github.com> wrote:
> 
> In integration-cli/docker_cli_attach_test.go:
> 
> > @@ -8,46 +9,81 @@ import (
> >  	"time"
> >  )
> >  
> > +const ATTACH_WAIT = 5 * time.Second
> This is not recommended style for constants in Go. Should be attachWait.
> 
> —
> Reply to this email directly or view it on GitHub <https://github.com/docker/docker/pull/7294/files#r16591930>.
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