remoting: make a gstreamer pipeline configurable

Allow a gstreamer pipeline to be configurable via an weston.ini. It is
necessary that source is appsrc, its name is "src", and sink name is
"sink" in pipeline. Also, remoting plugin ignore port and host
configuration if the gst-pipeline is specified.
2 jobs for remoting-gst-pipeline-configurable in 1 minute and 22 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Container Prep
passed #386593
container_prep

00:00:20

 
  Build
passed #386594
build-native-meson

00:01:01