Fix up NFS to use the new VirtualBox drivers

lib/vagrant/action/vm/nfs.rb

@@ -132,12 +132,17 @@ module Vagrant
         #
         # @return [String]
         def host_ip
-          interface = @env[:vm].vm.network_adapters.find do |adapter|
-            adapter.host_interface_object
+          @env[:vm].driver.read_network_interfaces.each do |adapter, opts|
+            if opts[:type] == :hostonly
+              @env[:vm].driver.read_host_only_interfaces.each do |interface|
+                if interface[:name] == opts[:hostonly]
+                  return interface[:ip]
+                end
+              end
+            end
           end
 
-          return nil if !interface
-          interface.host_interface_object.ip_address
+          nil
         end
 
         # Returns the IP address of the guest by looking at the first
@@ -145,7 +150,13 @@ module Vagrant
         #
         # @return [String]
         def guest_ip
-          @env[:vm].config.vm.network_options[1][:ip]
+          @env[:vm].config.vm.networks.each do |type, args|
+            if type == :hostonly && args[0].is_a?(String)
+              return args[0]
+            end
+          end
+
+          nil
         end
 
         # Checks if there are any NFS enabled shared folders.
@@ -161,7 +172,7 @@ module Vagrant
         def verify_settings
           raise Errors::NFSHostRequired if @env[:host].nil?
           raise Errors::NFSNotSupported if !@env[:host].nfs?
-          raise Errors::NFSNoHostNetwork if @env[:vm].config.vm.network_options.empty?
+          raise Errors::NFSNoHostNetwork if !guest_ip
         end
       end
     end

templates/locales/en.yml

@@ -450,8 +450,9 @@ en:
             are auto-detected, but can be overridden with `config.vagrant.host`.
             There is currently no host class loaded.
           no_host_network: |-
-            NFS shared folders requires that host only networking is enabled.
-            Please enable host only networking via `config.vm.network`.
+            NFS shared folders requires that host only networking is enabled
+            with a static IP. Please enable host only network and assign a
+            static IP via `config.vm.network`.
           not_supported: |-
             The host class is reporting that NFS is not supported by this host,
             or `nfsd` may not be installed. Please verify that `nfsd` is installed