Add a few new flags

[leforthomas]

Could we add a new flag to specify a SSH key to be used? eg --cloudsigma-ssh-key. Either the location on the client or a UUID to the cloudsigma key. This would save generating a new key each time and other benefits.

Also, could we add a flag(s) for machines which we want to be created within a VLAN and, possibly, without any public IP?

Expected Behavior

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Detailed Description

[pavel-github]

👋 @leforthomas,
good point about specifying ssh key and not generating a new one. I like this idea.
About flag(s) for machines running without public IPs. This is a little bit tricky because docker-machine does provisioning over SSH connection. I suggest that we use this issue to implement the feature with custom SSH key.