Rollback static routes upon router attribute update call failure on VSD.
Rollback static routes upon router attribute
update call failure on VSD.

Closes-Bug: OPENSTACK-1596

Change-Id: Ie04cd7cded20b4afa0886a3119217e3ffac18d6a

nuagenetworks/nuage-openstack-neutron,naveensan1/nuage-openstack-neutron,nuagenetworks/nuage-openstack-neutron,naveensan1/nuage-openstack-neutron