Avoid passing a generator expression to cache.get_many()

Generator expressions passed to the memcached backend's implementation of get_many() are exhausted prematurely. This results in KeyErrors when the backend tries to map keys returned by memcached back to keys passed by application code.

See https://github.com/django/django/blob/stable/1.8.x/django/core/cache/backends/memcached.py/#L99.

LEARNER-382

openedx/core/djangoapps/catalog/utils.py

@@ -53,7 +53,7 @@ def get_programs(uuid=None):
         if not uuids:
             logger.warning('Program UUIDs are not cached.')
 
-        programs = cache.get_many(PROGRAM_CACHE_KEY_TPL.format(uuid=uuid) for uuid in uuids)
+        programs = cache.get_many([PROGRAM_CACHE_KEY_TPL.format(uuid=uuid) for uuid in uuids])
         programs = list(programs.values())
 
         missing_uuids = set(uuids) - set(program['uuid'] for program in programs)