Make Backend::Local initialize compatible with Backend::Netssh

[seandilda]

This fix gives Backend::Local and Backend::Netssh the same initialize parameters. More specifically, this allows you to set
set :sshkit_backend, SSHKit::Backend::Local
in your config/deploy.rb for capistrano and have it successfully deploy locally.

[onceking]

Local#run also deviate from other backends.
others have

instance_exec(host, &@block)

but Local#run has:

instance_exec(&@block)

[AmirKremer]

Does changing it to

instance_exec(host, &@block)

Could do any harm?

[leehambley]

I'm not sure, honestly - if someone wants to feed back, I'd be happy to merge this, even if "deploy locally" is a bit of an illogical misnomer :)

[leehambley]

does anyone active in this thread have an interest in seeing it merged, or I would close the PR?

[seandilda]

I've worked around the workflow I was attempting by now. However, I'd still like to see it merged as it'd give me some useful deployment options going forward.

[leehambley]

Thanks @seandilda could you rebase the branch so it'll merge cleanly?

[mattbrictson]

I'm in the process of closing old/inactive PRs; pardon the noise. This PR seems to have been abandoned. Also, I think we're generally phasing out support for the local backend, so it probably would not be merged if it were submitted today.