rpcproxy is refactored into serverlist which prioritizes good servers
over servers in a remote DC or who have had a failure.
Registration, heartbeating, and alloc status updating will retry faster
when new servers are discovered.
Consul discovery will be retried more quickly when no servers are
available (eg on startup or an outage).
Reduce future confusion by introducing a minor version that is gossiped out
via the `mvn` Serf tag (Minor Version Number, `vsn` is already being used for
to communicate `Major Version Number`).
Background: hashicorp/consul/issues/1346#issuecomment-151663152
