packaging: setup: handling websocket_proxy rpm from websocketproxy plugin

Handling websocketproxy rpm from websocketproxy setup plugin.
The websocketproxy setup plugin is now able to install
the websocketproxy rpm if the user decide to configure it but
the rpm is not present.

Bug-Url: https://bugzilla.redhat.com/1140599

Change-Id: I1179ec04c3b24113de30b148fc3e04fc50e29c00
Signed-off-by: Simone Tiraboschi <stirabos@redhat.com>