dashboard: allow bgpvpns with the same name
dashboard: allow bgpvpns with the same name

The BGPVPN API allow to use a same name for
differents BGPVPNs.
The dashboard should allow the same behavior.

Change-Id: I749354c6f57051c6e895d97c31eb644d2af5f46b
Closes-Bug: 1699514

openstack/networking-bgpvpn,openstack/networking-bgpvpn,openstack/networking-bgpvpn