https://fedorahosted.org/sssd/ticket/1893

When SSSD is not enumerating (which is the default), we are trying to
link any "ghost" entries with a newly created user entry. However, when
enumeration is on, this means a spurious search on adding any user.

const char const * --> const char *const

Print warning if sysdb-tests or sysdb-ssh test are run
individually and LDB_MODULES_PATH was not set.

https://fedorahosted.org/sssd/ticket/1820

This prevents reportin false errors when internal functions return
a generic EINVAL or EACCES that should just be treated as internal
errors.

- Use a double-linked list for domains and subdomains.
- Never remove a subdomain, simply mark it as disabled if it becomes
  unused.
- Rework the way subdomains are refreshed.
  Now sysdb_update_subdomains() actually updates the current subdomains
  and marks as disabled the ones not found in the sysdb or add new ones
  found. It never removes them.
  Removal of missing domains from sysdb is deferred to the providers,
  which will perform it at refresh time, for the ipa provider that is
  done by ipa_subdomains_write_mappings() now.
  sysdb_update_subdomains() is then used to update the memory hierarchy
  of the subdomains.

- Removes sysdb_get_subdomains()
- Removes copy_subdomain()
- Add sysdb_subdomain_delete()

struct sss_domain_info is always used to represent domains now.
Adjust tests accordingly.

https://fedorahosted.org/sssd/ticket/1763