HONEYCOMB-369: configurable BGP peers

HONEYCOMB-369: configurable BGP peers

BGP peer configuration is no longer read from bgp-peer.json file.
Netconf/Restconf is can be used instead.
BGP peer configuration in HC follows openconfig-extensions model (as in ODL BGP):
* http://docs.opendaylight.org/en/stable-boron/user-guide/bgp-user-guide.html#bgp-peering
* http://docs.opendaylight.org/en/stable-boron/user-guide/bgp-user-guide.html#bgp-application-peer-and-programmable-rib

Change-Id: I91aa6c4fc0923edbacf6cd10abd3957569a4f8c6
Signed-off-by: Marek Gradzki <mgradzki@cisco.com>
(cherry picked from commit a3d562afdd96d4c37fe608af99f364e879ee92b6)