Avoids hardcoding magic numbers everywhere and self documents why a
mask is being applied.

In particular note that we merge ipa_account_info_netgroups_done()
and ipa_account_info_users_done() into a single fucntion called
ipa_account_info_done() that handles both cases

We also remove the auxiliary function ipa_account_info_complete() that
unnecessarily violates the tevent_req style and instead use a new function
named ipa_account_info_error_text() to generate error text.

Also do not intermix two tevent_req sequences

The check is now held only in ipa_get_subdomain_account_info_send().

This patch adds support for filtering attributes when constructing
attribute list from a map for LDAP query.

This is necessary because in several places in the code, we are
appending to the attrs returned from this value, and if we relied
on the map size macro, we would be appending after the NULL
terminator if one or more attributes were defined as NULL.