Title: #918: Add support for NSS hosts database lookup.
I have fixed the issues, but I have skipped adding the `ldap_iphost_*` options to
`src/config/etc/sssd.api.d/sssd-ipa.conf` because the resolver provider is not implemented
yet for the IPA backend. I don't know it very well and after having a quick look to
`src/providers/ipa/ipa_common.c` I am not sure if the schema is compatible with RFC2307
iphosts and there are design decisions to make like the CN to place the hosts. I will be
happy to implement it if required, but I would like to get this merged and implement the
netwoks lookup before.
See the full comment at https://github.com/SSSD/sssd/pull/918#issuecomment-592501897