core: Wait for container update after HTTP POST
core: Wait for container update after HTTP POST

Wait for updated signal from the parent container after pushing content
to a child item before returning an 'OK' to the client. This is needed to
satisfy the bogus check at the end of the DLNA CTT testcase 7.3.136.4.

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