Add winrm to the config_builder model

This adds the winrm attribute to the config_builder, so that the user,
password and other settings may be specified in a separate winrm.yaml,
when using the WinRM communicator.

    ---
    winrm:
      username: 'administrator'
      password: 'vagrant'
Merge pull request #26 from Iristyle/winrm-config-support

Add winrm to the config_builder model

Merged with a couple touch-ups to remove uneeded code.

Signed-off-by: Charlie Sharpsteen <source@sharpsteen.net>

Closes #26.