Title: #255: Use default configuration with missing sssd.conf
The problem I was considering was that before (in current master), if you compile sssd
with `--disable-files-domain` (which is the default), then you can't start sssd
without a config file. This patch changes this behaviour to start the implicit domain with
no config file, so what the option now does is adding the additional files domain even if
explicit domains are configured, right?
I'm not sure I would like that in RHEL. Although typically in RHEL, the order of
nsswitch modules is "files sss", so for files users, sss wouldn't be
typically reached at all..which might make the change OK..
See the full comment at https://github.com/SSSD/sssd/pull/255#issuecomment-299450895