user status: Restructure code.

We now have single function that handle both away
and not-away.

This refactoring sets us up to piggyback "info" more
easily onto status updates.

The only thing that changes here is that we don't
delete database rows any more when users revoke
their away status.  Instead we just set the status
to NORMAL.

zerver/lib/user_status.py

@@ -15,22 +15,20 @@ def get_away_user_ids(realm_id: int) -> Set[int]:
 
     return set(user_ids)
 
-def set_away_status(user_profile_id: int,
-                    client_id: int) -> None:
+def update_user_status(user_profile_id: int,
+                       status: int,
+                       client_id: int) -> None:
 
     timestamp = timezone_now()
-    status = UserStatus.AWAY
+
+    defaults = dict(
+        client_id=client_id,
+        timestamp=timestamp,
+    )
+
+    defaults['status'] = status
 
     UserStatus.objects.update_or_create(
         user_profile_id=user_profile_id,
-        defaults=dict(
-            client_id=client_id,
-            timestamp=timestamp,
-            status=status,
-        ),
+        defaults=defaults,
     )
-
-def revoke_away_status(user_profile_id: int) -> None:
-    UserStatus.objects.filter(
-        user_profile_id=user_profile_id,
-    ).delete()