Expose configuration to disable searching for Quagga

Right now in Nitrogen there are tons of errors and attempts flooding the log with over 150 retries to find quagga. This is unnecessary for users not using bgpvpn. There should be a configuration flag to disable using bgpvpn and searching for quagga. Also since there are retries, message should be a WARN and if final attempt fails then there should be an ERROR.

Examples in log:
2017-09-13 18:07:20,229 | ERROR | pool-46-thread-1 | BgpRouter | 298 - org.opendaylight.netvirt.bgpmanager-impl - 0.5.0 | Trying to connect BGP config server at 127.0.0.1 : 7644
2017-09-13 18:07:20,230 | INFO | pool-46-thread-1 | BgpConfigurationManager | 298 - org.opendaylight.netvirt.bgpmanager-impl - 0.5.0 | number of retries left 157 delay factor 23
2017-09-13 18:07:21,235 | ERROR | pool-46-thread-1 | BgpRouter | 298 - org.opendaylight.netvirt.bgpmanager-impl - 0.5.0 | Trying to connect BGP config server at 127.0.0.1 : 7644
2017-09-13 18:07:21,236 | INFO | pool-46-thread-1 | BgpConfigurationManager | 298 - org.opendaylight.netvirt.bgpmanager-impl - 0.5.0 | number of retries left 156 delay factor 24