Replace publisher name by URL

This allows to specify any amount of configuration option for each
publisher in each pipeline. UDP is the first to use this to possibly
publish to differents (host, port).

Blueprint: pipeline-publisher-url

Change-Id: I6a6f53ff438395c7bbbafad30efe097e1e01e1c6
Signed-off-by: Julien Danjou <julien@danjou.info>
Merge "Replace publisher name by URL"