hosts/linux: niceer error if rdesktop not found

lib/vagrant/errors.rb

@@ -396,6 +396,10 @@ module Vagrant
       error_key(:linux_nfs_mount_failed)
     end
 
+    class LinuxRDesktopNotFound < VagrantError
+      error_key(:linux_rdesktop_not_found)
+    end
+
     class LocalDataDirectoryNotAccessible < VagrantError
       error_key(:local_data_dir_not_accessible)
     end

plugins/hosts/linux/cap/rdp.rb

@@ -1,8 +1,14 @@
+require "vagrant/util/which"
+
 module VagrantPlugins
   module HostLinux
     module Cap
       class RDP
         def self.rdp_client(env, rdp_info)
+          if !Vagrant::Util::Which.which("rdesktop")
+            raise Vagrant::Errors::LinuxRDesktopNotFound
+          end
+
           args = []
           args << "-u" << rdp_info[:username]
           args << "-p" << rdp_info[:password] if rdp_info[:password]

templates/locales/en.yml

@@ -756,6 +756,10 @@ en:
         that the NFS client software is properly installed, and consult any resources
         specific to the linux distro you're using for more information on how to
         do this.
+      linux_rdesktop_not_found: |-
+        The `rdesktop` application was not found. Vagrant requires this
+        in order to connect via RDP to the Vagrant environment. Please ensure
+        this application is installed and available on the path and try again.
       machine_action_locked: |-
         An action '%{action}' was attempted on the machine '%{name}',
         but another process is already executing an action on the machine.