Proposal: standardise protocols

Let's standardise the way addrs are handles by swarm:

```
--------------                   ---------------------                   ----------------
| swarm join | ----------------> | discovery service | ----------------> | swarm manage |
--------------                   ---------------------                   ----------------
                                           |                             --------------
                                           ----------------------------> | swarm list |
                                                                         --------------
```

#### Swarm join

`swarm join` will support those formats:
* `tcp://<ip:port>`
* `http://<ip:port>`
* `https://<ip:port>`
* `<ip:port>` (`swarm` will transform this to `tcp://<ip:port>` before sending it the the discovery service)

Any other protocol will be denied

#### Swarm manage

`swarm manage` will work the same way as docker:
* `tcp://<ip:port>`: swarm will try to connect using `https` if the `--tls` otherwise `http`
* `http://<ip:port>`: swarm will always connect using `http`
* `https://<ip:port>`: swarm will always connect using `https`

#### Swarm list

`swarm list` will always display addrs with a protocol, either `tcp://`, `http://` or `https://`