Title: #182: cache_req: use rctx as memory context during midpoint refresh
Otherwise the tevent request is freed when we return data from cache_req
to caller. It is no big deal since the request is still finished on provider
side but the reply wouldn't be processed.
To pull the PR as Git branch:
git remote add ghsssd https://github.com/SSSD/sssd
git fetch ghsssd pull/182/head:pr182
git checkout pr182