Leak: RPC Client Connections

[abursavich]

It looks like all RPC connections are added to a map but not all connections are removed from the map. The leaky cases are when:

• there is an error reading the RPC type
• the type is not TLS and it is required
• the type is Raft
• the type is Multiplex
• the type is unrecognized

Only connections of the type Consul are removed from the map.

[armon]

Thanks for the report! We actually don't even need to bother track the clients. We were previously doing it to Close() the conn, but that will happen on Shutdown anyways.