Force the client_id to exist in the results from ProfileFetcher.

taar/profile_fetcher.py

@@ -22,6 +22,7 @@ class ProfileFetcher(object):
                      if not addon.get('is_system', False)]
 
         return {
+            "client_id": client_id,
             "geo_city": profile_data.get("city", ''),
             "subsession_length": profile_data.get("subsession_length", 0),
             "locale": profile_data.get('locale', ''),

tests/test_profile_fetcher.py

@@ -28,6 +28,7 @@ def test_profile_fetcher_returns_dict():
     # Note that active_addons in the raw JSON source is remapped to
     # 'installed_addons'
     assert fetcher.get("random-client-id") == {
+        "client_id": 'random-client-id',
         "bookmark_count": 0,
         "disabled_addons_ids": [],
         "geo_city": "Rome",