refactor StaticSourceRoute for better testability

changed the way this object is built such that most of the relevant
information is known at object creation time. This allows better
testability as the routing rules and ip rules generators can be
always accessed directly by tests.

Change-Id: If81c71b83670ee0c721dcce449e48ccc21e3bbec
Signed-off-by: ibarkan <ibarkan@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/34067
Reviewed-by: Dan Kenigsberg <danken@redhat.com>