engine: Added network provider parameters to UpdateVds

So that upon reinstallation a network provider could be
specified. Since now AddVds, UpdateVds and InstallVds parameters
needed the network provider parameters, moved the fields to their
common ancestor.

Change-Id: I0efdb7e4f76f44c06a4d14726b4f2016ada24bef
Signed-off-by: Lior Vernia <lvernia@redhat.com>