[SSSD] [sssd PR#906][opened] memcache: Stop using the word fastcache for memcache

[mzidek-rh]

   URL: https://github.com/SSSD/sssd/pull/906
Author: mzidek-rh
 Title: #906: memcache: Stop using the word fastcache for memcache
Action: opened

PR body:
"""
This patch removes the word fastche from our codebase.

We do not reffer to the fast in-memory mmaped cache consistantly.
Sometimes we call it fastcache, sometimes memcache and sometimes
mmap cache.

While we can not get rid of memcache, because it is rooted
in some config option names and in the documentation and
mmap cache is used a lot internally in our code, so getting
rid of that would require a lot of code changes, we can
easyly get rid of the 'fastcache' word because it is
only in a handful of places.

I think we should really stick to calling it memcache in
the documentation and debug messages and ideally also in
code comments to avoid confusion.
"""

To pull the PR as Git branch:
git remote add ghsssd https://github.com/SSSD/sssd
git fetch ghsssd pull/906/head:pr906
git checkout pr906