Hosts file auto-update

This piece of code will enable vagrant to auto-update the hosts file if
the hottsupdater plugin has been installed (this is required for this
to work!).

This takes out the fact that you manually have to edit your hosts file.
Code check for hostsupdater plugin

This change will check if the user has installed vagrant-hotstsupdater.
If it isn’t installed, it will not add the domains to the hosts file.