Different user and group lookup requests used nearly identical code,
this patch unifies some of the related code paths.

The task of get_my_domain_data() is to read some information about the
configured domain from the cache. While the sysdb interface was
redesigned some changes changed the behaviour so that the data of the
domain of the current request was read. If this domain is a sub-domain
the wrong data was read. As a result group-memberships of the configured
domain were not taken into account.

The original code didn't made it easy to see that always the parent
domain should be used here, because there was no comment indication this
and the function name get_my_domain_data() didn't made it clear either.
Additionally to fixing the issue this patch also adds a comment and
rename the function to get_parent_domain_data().

Fixes https://fedorahosted.org/sssd/ticket/1888

sss_mc_set_recycled is a static function, that should not
be used outside nsssrv_mmap_cache.c. The sss_cache tool
is an exception, because in the case when sssd is not running,
sss_cache must invalidate the memory cache file. That is why
sss_mc_set_recycled was copied to the tools_mc_util.c
(as helper function for sss_memcache_invalidate function).
It was duplicated to allow this function to remain static
(and invisible to any .h files), so that it is not used anywhere else.
Wrong usage of this function might cause race conditions and corrupt
the cache.

I'll add comments about the duplication to the code.

https://fedorahosted.org/sssd/ticket/1609

https://fedorahosted.org/sssd/ticket/1869

Currently the private data passed to the PAM request is a structure
allocated on the client context. But in the odd case where the back end
would be stopped or stuck until the idle timeout hits, the DP callback
would access data that were freed when the client timed out.

This patch introduces a new structure allocated on responder context,
whose only purpose is to live as long as the request is active.

https://fedorahosted.org/sssd/ticket/1864

Definition of structure sss_auth_token was removed from header file
authtok.h and there left only declaration of this structure.
Therefore only way how to use this structure is to use accessory function from
same header file.

To creating new empty authotok can only be used newly created function
sss_authtok_new(). TALLOC context was removed from copy and setter functions,
because pointer to stuct sss_auth_token is used as a memory context.

All declaration of struct sss_auth_token variables was replaced with
pointer to this structure and related changes was made in source code.

Function copy_pam_data can copy from argument src which was dynamically
allocated with function create_pam_data() or zero initialized struct pam_data
allocated on stack.

https://fedorahosted.org/sssd/ticket/1830

Function create_pam_data() should be only one way how to create new
struct pam_data, because it also initialize destructor to created
object.

https://fedorahosted.org/sssd/ticket/1575

The hierarchy is now:
main_ctx -> responder_ctx -> specific_ctx

where specific_ctx is one of sudo, pam, etc.