* refactor nxos_system * refactor nxos_user * refactor nxos_vlan * refactor nxos_vrf
* fix issues with python3.x * Add integration testa and fix for nxos_evpn_vni * add nxos_evpn_vni to nxos.yaml * fix get_vtp_config() * add new integration tests * fix rollback * add integration test files