fixed windows compatibility issues for the hosts file

hi Shawn, great job on this plugin :)

I found some windows compatibility issue that i fixed.
the hostsfile::update_host didn't deal with a windows based environment, so i added a small if statement.
another thing, that might be a windows thing, but i have no idea, because on a single-vm it worked, but when i added more VMs, it started to happen... in hostfile::update_guest i got error on FileUtils.rm that says that there is no file/directory on the /etc/hosts file. so i added a rescue statement.