Bug 23173: (follow-up) Display available partners

Bug 23173: (follow-up) Display available partners

When selecting partners for search during the "Place request with
partner libraries" workflow, there was no indication of which partners
could actually be searched (i.e. are attached to a Z target and enabled
for partner search). We now list them

Signed-off-by: Niamh Walker-Headon <Niamh.Walker-Headon@tudublin.ie>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>