Prevent an empty resources: list if no listener_resources defined

This was causing worker_listener blocks to get generated with
Nonetype resources, crashing things. This was only a problem for
worker types that don't have any configured resources.

docker/conf/worker.yaml.j2

@@ -13,8 +13,10 @@ worker_replication_http_port: 9093
 worker_listeners:
   - type: http
     port: {{ port }}
+{% if listener_resources %}
     resources:
       - names:
 {%- for resource in listener_resources %}
         - {{ resource }}
 {%- endfor %}
+{% endif %}

docker/configure_workers_and_start.py

@@ -271,7 +271,7 @@ def generate_worker_files(environ, config_path: str, data_dir: str):
         worker_types = []
     elif worker_types == "*":
         # Use all known worker types
-        worker_types = WORKERS_CONFIG.keys()
+        worker_types = list(WORKERS_CONFIG.keys())
     else:
         # Split type names by command
         worker_types = worker_types.split(",")