frontend: fluent API instead of temporary fields

This patch replace the usage of temporary fields with fluent API - where
setters return a reference to "this" which can be used to make
further calls on the return value of the setter method.

Not all setters were changed in this patch of course, only those that
were relevant to simplify the code which is related to run-once
capability (this patch is part of few patches that were done lately to
refactor the areas around run-once capability in the frontend)

This patch also includes:
1. remove the auto-assign entity setting which is not needed because it
is already done in WebadminRunOnceModel#init method
2. move the duplicate code of display protocol settings in run-once
mode from UserPortalListModel and VmListModel to be just in RunOnceModel

Change-Id: I52bfe6b084ecc0643a5a45a1fb9a1170b415ed15
Signed-off-by: Arik Hadas <ahadas@redhat.com>