Support the Vagrant::Hostsupdater plugin

Updates the Vagrantfile to set up the correct hosts entries and also
updates the README to cover installations where Hostsupdater is
installed.
add a hosts entry for the main virtualhost
Check if the hostsupdater plugin exists before configuring it.
Merge pull request #45 from akrabat/support-hostsupdater

Support the Vagrant::Hostsupdater plugin
Merge pull request #46 from lornajane/host-file-entries

add a hosts entry for the main virtualhost