Required for:
https://fedorahosted.org/sssd/ticket/2637

This is a first step towards making it possible for domain to be around,
but not contacted by Data Provider.

Also explicitly create domains as active, previously we only relied on
talloc_zero marking dom->disabled as false.

Reviewed-by: Pavel Březina <pbrezina@redhat.com>

Reviewed-by: Pavel Březina <pbrezina@redhat.com>

Move copy pasted code for converting sockaddr_storage to string into
function.

Resolves:
https://fedorahosted.org/sssd/ticket/2495

Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>

Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>

Uses the ipa-getkeytab call to retrieve keytabs for one-way trust
relationships.

https://fedorahosted.org/sssd/ticket/2636

Reviewed-by: Sumit Bose <sbose@redhat.com>

Allows to distinguish the trust directions for trusted domains. For
domains where we don't know the direction in server mode, we assume
two-way trusts.

Member domains do not have the direction, but rather the forest root
direction is used.

Reviewed-by: Sumit Bose <sbose@redhat.com>

Resolves:
https://fedorahosted.org/sssd/ticket/2583

Reviewed-by: Michal Židek <mzidek@redhat.com>

The function sss_strerror() should not return a sentence.
It shoudl return string; the same as strerror()

Reviewed-by: Pavel Březina <pbrezina@redhat.com>

This function decomposes object path into array of strings. The
"_exact" version expects a certain number of parts otherwise an
error is thrown.

Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>

Not all user groups need to be resolved if group deny list is empty.

Resolves:
https://fedorahosted.org/sssd/ticket/2519

Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>