Add interactive shell for celery tasks

That's pretty useful for developing new tasks or just running one-off
tasks.

scripts/celery_shell.py

@@ -1,8 +1,32 @@
-from scripts.db_shell import *
+"""
+Run this script from galaxy's root with
+```
+ipython -i scripts/celery_shell.py -- -c config/galaxy.yml
+```
+"""
+import logging
+import os
+
+WARNING_MODULES = ['parso', 'asyncio', 'galaxy.datatypes']
+for mod in WARNING_MODULES:
+    logger = logging.getLogger(mod)
+    logger.setLevel('WARNING')
+
+from scripts.db_shell import config
+os.environ['GALAXY_CONFIG_FILE'] = os.environ.get('GALAXY_CONFIG_FILE', config['config_file'])
 
 from galaxy.celery import get_galaxy_app
+from galaxy.celery import tasks  # noqa: F401
 
-from galaxy.celery.tasks import *
+HELP = """
+============
+Run celery tasks interactively.
+tasks are collected in task module.
+
+To run recalculate_user_disk_usage for user 1 in a celery worker
+type
+>>> tasks.recalculate_user_disk_usage.deley(user_id=1)
+"""
 
 app = get_galaxy_app()
-assert app, 'Set GALAXY_CONFIG_FILE to the path of your galaxy.yml file'
+print(HELP)