BUG-2109 : cleaned BGP sessions on session closed.

Added proper close from BGP peer. Negotiation failed method now called from both sub and superclass.

Change-Id: I83e922df826c7fbb9130ca637d2dfe99d3e93a27
Signed-off-by: Dana Kutenicsova <dkutenic@cisco.com>
Merge "BUG-2109 : cleaned BGP sessions on session closed."