[j-nsp] Keep local VPLS instance up when there are no remote PEs up

[Chuck Anderson]

In a VPLS multihoming scenario, if the remote primary multihomed PE
goes down, the local PE should start forwarding traffic to the CE:

https://www.juniper.net/documentation/en_US/junos15.1/topics/concept/vpn-vpls-multihoming-network-failures.html

But if all remote PEs go down (or if there are only 2 PEs in the VPLS
routing-instance to begin with, and one goes gown), the local VPLS
instance goes down, showing "No connections found".  The local IRB &
CE interfaces are taken down as well.

How do I keep the local VPLS instance UP including keeping the local
IRB and CE interfaces UP in this scenario?  "connectivity-type irb" or
"permanent" is about keeping the instance UP when all local CE
interfaces go down--I need the opposite, the CEs are up but remote PEs
are down.

Thanks.