Also simplify sdap_access_send to avoid completely fake _send() routines.

Simplifies and consolidates error reporting for ldap authentication paths.

Adds 3 new error codes:
    ERR_CHPASS_DENIED  - Used when password constraints deny password changes
    ERR_ACCOUNT_EXPIRED  - Account is expired
    ERR_PASSWORD_EXPIRED  - Password is expired

https://fedorahosted.org/sssd/ticket/1819

https://fedorahosted.org/sssd/ticket/1795

Only alpha-numeric chars, dashes and underscores are allowed in
krb5 include directory.

https://fedorahosted.org/sssd/ticket/1804

Fixes https://fedorahosted.org/sssd/ticket/1766

- 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.