providers/docker: better error on suspend

plugins/providers/docker/action.rb

@@ -283,6 +283,12 @@ module VagrantPlugins
         end
       end
 
+      def self.action_suspend
+        lambda do |env|
+          raise Errors::SuspendNotSupported
+        end
+      end
+
       # The autoload farm
       action_root = Pathname.new(File.expand_path("../action", __FILE__))
       autoload :Build, action_root.join("build")

plugins/providers/docker/errors.rb

@@ -37,6 +37,10 @@ module VagrantPlugins
         error_key(:state_stopped)
       end
 
+      class SuspendNotSupported < DockerError
+        error_key(:suspend_not_supported)
+      end
+
       class SyncedFolderNonDocker < DockerError
         error_key(:synced_folder_non_docker)
       end

templates/locales/providers_docker.yml

@@ -185,6 +185,11 @@ en:
             d.remains_running = false
           end
 
+      suspend_not_supported: |-
+        The "suspend" command is not supported with the Docker provider.
+        Docker containers don't natively support suspend. If you're using
+        a host machine, you can suspend the host machine by finding it
+        in `vagrant global-status` and using `vagrant suspend <id>`.
       synced_folder_non_docker: |-
         The "docker" synced folder type can't be used because the  provider
         in use is not Docker. This synced folder type only works with the