Fix references to dotcloud repo.

Fixes running tests in clean environment.

```
go test ./...
# github.com/docker/libchan
inmem_test.go:9:2: cannot find package "github.com/dotcloud/docker/pkg/testutils" in any of:
	/Users/pnasrat/Library/homebrew/Cellar/go/1.3/libexec/src/pkg/github.com/dotcloud/docker/pkg/testutils (from $GOROOT)
	/Users/pnasrat/go/src/github.com/dotcloud/docker/pkg/testutils (from $GOPATH)
FAIL	github.com/docker/libchan [setup failed]
# github.com/docker/libchan/unix
inmem_test.go:9:2: cannot find package "github.com/dotcloud/docker/pkg/testutils" in any of:
	/Users/pnasrat/Library/homebrew/Cellar/go/1.3/libexec/src/pkg/github.com/dotcloud/docker/pkg/testutils (from $GOROOT)
	/Users/pnasrat/go/src/github.com/dotcloud/docker/pkg/testutils (from $GOPATH)
FAIL	github.com/docker/libchan/unix [setup failed]
# github.com/docker/libchan/utils
inmem_test.go:9:2: cannot find package "github.com/dotcloud/docker/pkg/testutils" in any of:
	/Users/pnasrat/Library/homebrew/Cellar/go/1.3/libexec/src/pkg/github.com/dotcloud/docker/pkg/testutils (from $GOROOT)
	/Users/pnasrat/go/src/github.com/dotcloud/docker/pkg/testutils (from $GOPATH)
FAIL	github.com/docker/libchan/utils [setup failed]
ok  	github.com/docker/libchan/data	0.006s
ok  	github.com/docker/libchan/http2	0.045s
```