When a solicited leafnode comes from multiple servers that themselves are a cluster, cycles were formed.
This change allows solicited leafnodes to behave similar to gateways in that each server of a cluster
is expected to have a solicted leafnode per destination account and cluster.
We no longer forward subscription interest or messages to a cluster from a server that has a solicited leafnode.
Signed-off-by: Derek Collison <derek@nats.io>