BUG-2400 : Memory optimizations for AS-Path and Origin attributes

- AS-Path: minimized empty lists
- Origin: reusing Origin container

Change-Id: I424169873ad1bfae0e3cd928bf285f59c70141ec
Signed-off-by: Dana Kutenicsova <dkutenic@cisco.com>
(cherry picked from commit 6954a433170a38623f5e7621f0821d6cfcb6c6be)
Merge "BUG-2400 : Memory optimizations for AS-Path and Origin attributes" into stable/helium