Fixes GetStreamUriRequest, log_switch

Hello! I have two minor improvements.

 1. [log_switch](https://github.com/turboladen/log_switch) 1.0 introduced breaking changes, so I've pinned the gemspec on 0.4 (the last working version).
 2. In trying to get stream URIs from some Avigilon devices, I noticed a discrepency between this gem and the ONVIF spec.
   * The [Media Service Spec (pdf)](http://www.onvif.org/specs/srv/media/ONVIF-Media-Service-Spec-v210.pdf) uses `StreamType` instead of `Stream` for the `StreamSetup` element of a `GetStreamUriRequest`.
   * Sending an empty `Tunnel` element actually breaks the request. So my changes omit that element if it has no contents.

Thanks!