allow StartContainer to accept bind mounts

without this change, it is impossible to specify bind mounts via this
API.

example:
```Go
d.StartContainer(c.ID, &docker.HostConfig{
	Binds: []string{"data:/var/lib/postgresql"},
})
```
adjust test to use the new StartContainer api
Merge pull request #30 from srid/bind_mounts

allow StartContainer to accept bind mounts