Make namespace deletion asynchronous

Instead of deleting a namespace synchronously as before, we now mark the namespace for deletion, disable it, and rename it. A worker then comes along and deletes the namespace in the background. This results in a *significantly* better user experience, as the namespace deletion operation now "completes" in under a second, where before it could take 10s of minutes at the worse.

Fixes https://jira.coreos.com/browse/QUAY-838

workers/namespacegcworker.py

@@ -0,0 +1,28 @@
+import logging
+import time
+
+from app import app, namespace_gc_queue, all_queues
+from data import model
+from workers.queueworker import QueueWorker, JobException
+from util.log import logfile_path
+
+logger = logging.getLogger(__name__)
+
+
+POLL_PERIOD_SECONDS = 60
+
+
+class NamespaceGCWorker(QueueWorker):
+  """ Worker which cleans up namespaces enqueued to be GCed.
+  """
+  def process_queue_item(self, job_details):
+    logger.debug('Got namespace GC queue item: %s', job_details)
+    marker_id = job_details['marker_id']
+    model.user.delete_namespace_via_marker(marker_id, all_queues)
+
+if __name__ == "__main__":
+  logging.config.fileConfig(logfile_path(debug=False), disable_existing_loggers=False)
+
+  logger.debug('Starting namespace GC worker')
+  worker = NamespaceGCWorker(namespace_gc_queue, poll_period_seconds=POLL_PERIOD_SECONDS)
+  worker.start()