possible for task queue to be locked up
### Observed behavior

When server starts, task queue might have items in it even if there are none running

### Expected behavior

task queue should be cleared when server starts

### User-facing consequences

Incorrect view of server state and potentially blocked from performing actions

### Steps to reproduce

(Is this correct?)

* start server
* start loading channel metadata
* kill server
* start server

### Context

* Kolibri version: 0.7 beta

diff --git a/kolibri/utils/server.py b/kolibri/utils/server.py
index 497f8ffd11..ffe1a4c66f 100644
--- a/kolibri/utils/server.py
+++ b/kolibri/utils/server.py
@@ -68,6 +68,11 @@ def start(port=8080):
     from kolibri.content.utils.annotation import update_channel_metadata
     update_channel_metadata()
 
+    # This is also run every time the server is started to clear all the tasks
+    # in the queue
+    from kolibri.tasks.client import get_client
+    get_client().clear(force=True)
+
     def rm_pid_file():
         os.unlink(PID_FILE)
 
['kolibri/utils/server.py']