build: Correct sysconfdir for uninstalled case
build: Correct sysconfdir for uninstalled case

Use 'data' directory in source tree as the system config location when
configured to run uninstalled.

GNOME/rygel,Pelagicore/Media-Manager-Rygel-patched,GNOME/rygel,Pelagicore/Media-Manager-Rygel-patched,Pelagicore/Media-Manager-Rygel-patched,jku/rygel,luisbg/rygel,jku/rygel,Tarnyko/rygel,GNOME/rygel,Tarnyko/rygel