Allow a proc/lambda for knife[:winrm_password]

[docwhat]

Our Administrator passwords vary per machine (for best security). It would be nice if we could use a callback for knife[:winrm_password] so that we could look up the password (it's in a yaml file that becomes a databag, but other users might want to look it up some other way) on a per machine basis.

I'm imagining something like:

def lookup_admin_password(node_name):
  YAML.load('my_passwords.yml')[node_name]
end

knife[:winrm_user] = 'Administrator'
knife[:winrm_password] = method(:lookup_admin_password)

[docwhat]

I also ran across another use case: changing the winrm_port and winrm_transport based on node attributes, since not all nodes use HTTPS at the moment.