Adds check for SSH keygen command
Adds check for SSH keygen command

Adds a check to find ssh-keygen in the user's $PATH, in the event it
can't find it, return an error with a friendly message

Signed-off-by: Simon Thulbourn <a35c15f375c4f69af4708338068f3913eefbe66d@thulbourn.com>

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