webadmin: Simplify mapping in Setup Networks initialization

Some mapping was performed in two steps, first from one entity's name
to another entity's name, and then from the second entity's name to
the entity itself, so I removed the intermediary phase. Another map
was actually used as a collection, so changed it to a list.

Change-Id: Ia29636b437262301996a459f017d2260680e708f
Signed-off-by: Lior Vernia <lvernia@redhat.com>