Use Omnibus copy/delete on Windows instead of cp/rm

Using cp would presume we're running under MinGW, which is not currently
installed on the build slaves by https://github.com/opscode-cookbooks/omnibus
Merge pull request #264 from opscode/btm/libyaml-windows-cp

Use FileUtils.cp on Windows instead of cp
Create libyaml-windows directory at build time, not compile
Create openssl-windows directory at build time, not compile