BUG-353: add remote-as awareness

This adds the configuration knob for the remote AS. Furthermore it adds
validation of the AS advertizement during negotiation. Drive-by fixes
include introduction of buildErrorNotify() and rename of fields inside
BGPObjectComparator for clarity.

Change-Id: Ie60e0633d84a8a6a239517600e4666dee2a0d3ed
Signed-off-by: Robert Varga <rovarga@cisco.com>
Signed-off-by: Dana Kutenicsova <dkutenic@cisco.com>