[Schema transformer] Do not delete default routing instance
[Schema transformer] Do not delete default routing instance

As the virtual network default routing instance deletion is handled
by the vnc api now, the schema should no remove it to prevent race
between us.

Change-Id: I27fa429ef6b0f547859db1ab5c29a699db7441e7
Closes-bug: #1580510

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