Host os hosts file

This set of changes was made to manage hosts file entries on the host machine. This is so that you can use the hostnames to connect to your local boxes.

As part of this, I changed it so that we actually fetch the existing hosts file from the guest machines and add to it rather than overwriting.

Keywords added: hostmanager.manage_local = true 
Manage local hosts file

Caveats:
- Assumes that you need sudo to modify your local /etc/hosts file, I am planning on making this a configuration parameter in the near future.
- It's assuming your hosts file is /etc/hosts, so it won't work with windows.