packaging: setup: getting a cert for a remote wsp via support files

Providing support to get the certificate for a remote Websocket Proxy
also via support files and not just only with copy and paste.
Adding pasted cert validation and better error handling.

Change-Id: I24384e213470ff521a8a3651920fef594e4d7c9d
Bug-Url: https://bugzilla.redhat.com/1116017
Signed-off-by: Simone Tiraboschi <stirabos@redhat.com>