Refactor 4 different renderings of task description

[benclifford]

Prior to this PR, there were 4 variant ways to render a future (which is usually but not always a Parsl task) as a text string:

1. describing failure of inner future in a join_app with 1 future to join

• rendered task ID if the inner future has a task record attribute, without checking it is a parsl.dataflow.taskrecord.TaskRecord or that that attribute contains a task id entry.
• otherwise render as None

2. describing failure of inner future in a join_app with a list of futures to join

• is meant to do the same as case 1, but is buggy and always renders as None (the wrong object is checked for having a task_record attribute)

3. describing failure of a dependency future

• rendered task ID if there was a task_record, and the
  future is from the same DFK as is rendering the code
  (so that a task number from a different DFK is not
  rendered, in the corner case of a task from one DFK
  being used as a dependency for a task in another DFK)

• otherwise, renders the repr of the future

4. describing which dependencies will be waited on when submitting a task to the DFK

• rendered task ID if the future is an instance of AppFuture or DataFuture
• otherwise renders the repr of the future

This PR makes a single render method. It is a member of the DFK, because rendering is done in the context of the DFK: two parsl task AppFutures will be rendered differently if they are from this DFK or a different DFK.

This PR implements render_future_description which tries to combine all of the above:

• if the future is an AppFuture, and is from the same
  DFK, render the task ID
• otherwise render the repr of the future

Changed Behaviour

human readable descriptions of dependencies/join inner futures will be changed

Fixes

Fixes # (issue)

Type of change

Choose which options apply, and delete the ones which do not apply.

• Bug fix
• New feature
• Update to human readable text: Documentation/error messages/comments
• Code maintenance/cleanup

[khk-globus]

Nice improvement.