Fixes: Modified BGP AS number not reflecting in the default-domain:admin:public:service-xxx and default-domain:demo:snat-si-left_snat_xxxx routing instances
Fixes: Modified BGP AS number not reflecting in the default-domain:admin:public:service-xxx
and default-domain:demo:snat-si-left_snat_xxxx routing instances

Updating the ASN from the global route target list instead of updating from the routing
instance. Moved the update function from VirtualNetwork to GlobalSystemConfig, since
the function will be called for every network which is not necessary.

Change-Id: Iabb30a94c8e127d6e59c19c85d2547731f017079
Closes-Bug:1603857

eonpatapon/contrail-controller,nischalsheth/contrail-controller,nischalsheth/contrail-controller,eonpatapon/contrail-controller,nischalsheth/contrail-controller,rombie/contrail-controller,eonpatapon/contrail-controller,nischalsheth/contrail-controller,rombie/contrail-controller,rombie/contrail-controller,eonpatapon/contrail-controller,eonpatapon/contrail-controller,rombie/contrail-controller,nischalsheth/contrail-controller,rombie/contrail-controller,eonpatapon/contrail-controller,eonpatapon/contrail-controller,rombie/contrail-controller,nischalsheth/contrail-controller,nischalsheth/contrail-controller,nischalsheth/contrail-controller,rombie/contrail-controller