Do not discard exceptions thrown during sftp close

[henryxparker]

I have been having some connection issues, and I believe the .attempt.flatmap(_ => ...) may have been throwing away a useful exception.

The previous code seems to be using that attempt to ensure that the ssh client gets disconnected at the end, but that is precisely the function of Resource.

I have a feeling I might be missing some deliberate choice that originally went into this, but I suppose only @regis-leray can answer that.

[regis-leray]

@henryxparker your implementation, force the user to catch any possible problem if during the connection close process it failed. I would assume it is ok, they will be able to discard the error.

Thanks again for your contribution. if build passed it will be merge

[regis-leray]

@henryxparker the build failed, fix it when you have time. Thank you