client: make content-base better
client: make content-base better

Use the URI formatting functions to make a content-base. Also make sure that
there is a trailing / at the end.

barisdemiray/gst-rtsp-server,thaytan/gst-rtsp-server,surround-io/gst-rtsp-server,Lachann/gst-rtsp-server,hsteinhaus/gst-rtsp-server,barisdemiray/gst-rtsp-server,surround-io/gst-rtsp-server,Lachann/gst-rtsp-server,thaytan/gst-rtsp-server,thaytan/gst-rtsp-server,hsteinhaus/gst-rtsp-server,hsteinhaus/gst-rtsp-server,Lachann/gst-rtsp-server,surround-io/gst-rtsp-server,barisdemiray/gst-rtsp-server