Automatic SSH tunneling with Deploy credentials file

[yusefnapora]

This adds a --deployCredentialsFile option that you can point at the file downloaded at the end of the Deploy process. If given, it will create an SSH tunnel for you to the remote machine, using the ip address, username and password from the file. It uses a javascript SSH implementation, so it should work on Windows.

To get this to work, I made a subcommand helper function that wraps each subcommand handler. If an SSH config is given, it creates the tunnel, runs the handler, then closes the tunnel afterwards. The subcommand handler functions had to be tweaked slightly to return a Promise, which the wrapper waits on before closing the tunnel.

I also made the subcommand helper create the RestClient instance, so subcommands can just pull the client member out of their options object, instead of grabbing apiUrl and creating a RestClient. That may come in handy if we ever add more options to the RestClient constructor, since we can just update it in one place.

example:

mcclient --deployCredentialsFile ~/Downloads/mediachain_node_138.68.24.97.yaml id
Peer ID: QmcrFvafCC64F44vhzv2JsYLYdLf3N2FHHiVjajDXrLhFh
Publisher ID: 4XTTMGc59GywZVY3gipX9nJNeWeW9bFN4h8ui61Q9vKvBM97m
Info: hello world

For this to be truly great, I'd like to add persistent configuration to mcclient, so we can store the credentials in e.g. ~/.mediachain/mcclient/config.json. Then we wouldn't need to require the --deployCredentialsFile option for every command. That seems like it belongs in its own PR though.

Closes #92

[denisnazarov]

Awesome, working for me 👍

[vyzo]

yusef, let's use ssh keys -- using passwords is a very bad idea.

[parkan]

how did we end up with yaml, just the deploy default?

[yusefnapora]

yeah, that was mostly just laziness on my part. I'd be happy to change the deploy side to JSON, and possibly change the format so that it matches the options for tunnel-ssh more closely.

[parkan]

I'd prefer to avoid config format proliferation this early in the process, even if yaml and JSON can technically the equivalent

[parkan]

would put this in an else block on 119 to make it clearer

[parkan]

was going to say that you can just write this as .catch(err => ...).then(closeTunnel) but I guess not if you want to rethrow... I wonder what byzantine reasons exist for finally not making it into the spec

my only nitpick here is the use of Promise.resolve() in what is clearly an error context (e.g. https://github.com/mediachain/aleph/pull/99/files#diff-d697977bdb0d2a7923a62aaffcc24d13R28)

[yusefnapora]

Yeah, I wasn't happy about that either. I think the right thing to do is have the command handlers just throw on error conditions and have the subcommand helper be responsible for printing errors to the console, cleaning up and exiting the process.

[parkan]

Agreed