Rename misnamed dependency launch thread (#4012)

While the original work which introduced this (PR #3478) was aimed at
fixing a stack depth bug to do with dependency task launches, this
thread is actually used for *all* task launches.

# Changed Behaviour

thread name in log file will be new name

## Type of change
- Update to human readable text: Documentation/error messages/comments

Author: benclifford

parsl/dataflow/dflow.py

@@ -190,7 +190,7 @@ def __init__(self, config: Config) -> None:
         self.tasks: Dict[int, TaskRecord] = {}
         self.submitter_lock = threading.Lock()
 
-        self.dependency_launch_pool = cf.ThreadPoolExecutor(max_workers=1, thread_name_prefix="Dependency-Launch")
+        self._task_launch_pool = cf.ThreadPoolExecutor(max_workers=1, thread_name_prefix="Task-Launch")
 
         self.dependency_resolver = self.config.dependency_resolver if self.config.dependency_resolver is not None \
             else SHALLOW_DEPENDENCY_RESOLVER
@@ -608,7 +608,7 @@ def launch_if_ready(self, task_record: TaskRecord) -> None:
         launch_if_ready is thread safe, so may be called from any thread
         or callback.
         """
-        self.dependency_launch_pool.submit(self._launch_if_ready_async, task_record)
+        self._task_launch_pool.submit(self._launch_if_ready_async, task_record)
 
     @wrap_with_logs
     def _launch_if_ready_async(self, task_record: TaskRecord) -> None:
@@ -1203,9 +1203,9 @@ def cleanup(self) -> None:
             self.monitoring.close()
             logger.info("Terminated monitoring")
 
-        logger.info("Terminating dependency launch pool")
-        self.dependency_launch_pool.shutdown()
-        logger.info("Terminated dependency launch pool")
+        logger.info("Terminating task launch pool")
+        self._task_launch_pool.shutdown()
+        logger.info("Terminated task launch pool")
 
         logger.info("Unregistering atexit hook")
         atexit.unregister(self.atexit_cleanup)