Add option to print task IDs to qinfo

Option to print IDs (PIDs) of running clusters added to qinfo.
This provides an easy way for scripts and process managers to fetch the PID(s) of running clusters.

django_q/monitor.py

@@ -187,3 +187,14 @@ def info(broker=None):
           term.white('{0:.4f}'.format(exec_time))
           )
     return True
+
+
+def get_ids():
+    # prints id (PID) of running clusters
+    stat = Stat.get_all()
+    if stat:
+        for s in stat:
+            print(s.cluster_id)
+    else:
+        print('No clusters appear to be running.')
+    return True