You're viewing the documentation for the experimental version of Vagrant (the 1.x series). The current stable series is 1.0.x and the documentation can be found here. You can learn more about the Vagrant versioning scheme here.
Configuration key: config.vm.host_name
Default value: nil
This can be set to the host name you wish the guest machine to have. Vagrant will automatically execute the configuration necessary to make this happen. Example:
Vagrant::Config.run do |config|
# ...
config.vm.host_name = "pablo"
end