Prefer xfreerdp for RDP connections on Linux hosts.

Rather than only using rdesktop (which does not work properly with newer
versions of RDP), use xfreerdp if available and fall back to rdesktop if
not.

plugins/hosts/linux/cap/rdp.rb

@@ -5,17 +5,35 @@ module VagrantPlugins
     module Cap
       class RDP
         def self.rdp_client(env, rdp_info)
-          if !Vagrant::Util::Which.which("rdesktop")
-            raise Vagrant::Errors::LinuxRDesktopNotFound
-          end
+          # Detect if an RDP client is available.
+          # Prefer xfreerdp as it supports newer versions of RDP.
+          rdp_client =
+            if Vagrant::Util::Which.which("xfreerdp")
+              "xfreerdp"
+            elsif Vagrant::Util::Which.which("rdesktop")
+              "rdesktop"
+            else
+              raise Vagrant::Errors::LinuxRDesktopNotFound
+            end
 
           args = []
-          args << "-u" << rdp_info[:username]
-          args << "-p" << rdp_info[:password] if rdp_info[:password]
-          args += rdp_info[:extra_args] if rdp_info[:extra_args]
-          args << "#{rdp_info[:host]}:#{rdp_info[:port]}"
 
-          Vagrant::Util::Subprocess.execute("rdesktop", *args)
+          # Build appropriate arguments for the RDP client.
+          case rdp_client
+          when "xfreerdp"
+            args << "/u:#{rdp_info[:username]}"
+            args << "/p:#{rdp_info[:password]}" if rdp_info[:password]
+            args << "/v:#{rdp_info[:host]}:#{rdp_info[:port]}"
+            args += rdp_info[:extra_args] if rdp_info[:extra_args]
+          when "rdesktop"
+            args << "-u" << rdp_info[:username]
+            args << "-p" << rdp_info[:password] if rdp_info[:password]
+            args += rdp_info[:extra_args] if rdp_info[:extra_args]
+            args << "#{rdp_info[:host]}:#{rdp_info[:port]}"
+          end
+
+          # Finally, run the client.
+          Vagrant::Util::Subprocess.execute(rdp_client, *args)
         end
       end
     end