Use host capability to update key file permissions if available

plugins/communicators/ssh/communicator.rb

@@ -194,17 +194,9 @@ module VagrantPlugins
             f.write(priv)
           end
 
-          # Adjust private key file permissions
-          if Vagrant::Util::Platform.windows?
-            begin
-              priv_path = @machine.data_dir.join("private_key").to_s
-              File.set_permissions(priv_path, Etc.getlogin => File::FULL)
-            rescue => e
-              @logger.warn("Error encountered during private key permissions set - " \
-                "#{e.class}: #{e.message}")
-            end
-          else
-            @machine.data_dir.join("private_key").chmod(0600)
+          # Adjust private key file permissions if host provides capability
+          if @machine.env.host.has_capability?(:set_ssh_key_permissions)
+            @machine.env.host.capability(:set_ssh_key_permissions, @machine.data_dir.join("private_key"))
           end
 
           # Remove the old key if it exists