Currently, if an acceptor peer deletes a peering the dialer's peering
will eventually get to a "terminated" state. If the two clusters need to
be re-peered the acceptor will re-generate the token but the dialer will
encounter this error on the call to establish:
"failed to get addresses to dial peer: failed to refresh peer server
addresses, will continue to use initial addresses: there is no active
peering for "<<<ID>>>""
This is because in `exchangeSecret().GetDialAddresses()` we will get an
error if fetching addresses for an inactive peering. The peering shows
up as inactive at this point because of the existing terminated state.
Rather than checking whether a peering is active we can instead check
whether it was deleted. This way users do not need to delete terminated
peerings in the dialing cluster before re-establishing them.
