Allow user to disable SSL peer ceritifcate validation

This works with commits to the em-winrm (https://github.com/gswallow/em-winrm/commit/75eb847c6b2cdf09b6c6e7b4cfa3f69d9c45f47a) and knife-windows (https://github.com/gswallow/knife-windows/commit/d04c835cfff1260017b91a799168e90b931cad6a) gems.