packaging: setup: Use common code for remote wsp pki

Code to handle PKI stuff with remote engine has been moved
to a common place to be shared between different plugins.
Using it.

Change-Id: Id72711fb1577d5ee97454a36650456c2675206be
Bug-Url: https://bugzilla.redhat.com/1125188
Signed-off-by: Simone Tiraboschi <stirabos@redhat.com>