Add :endpoint to the options hash for Local Storage

If endpoint is nil, files loaded to Local Storage 
have a public_url of nil. Specifying a value for :endpoint
in the options hash fixes this.

Also please see my comment on 

https://github.com/fog/fog/commit/61ff93af32b76009651092cbd297a271b182b97e

Seeing this in the documentation would have saved me a couple of hours.

Not sure the pull request is appropriate - just thought it would make my suggested change very clear.

Thanks!