LDAP: Bind to the LDAP server also in the auth
    
    When dealing with id_provider not being the same as auth_provider, SSSD
    has to bind the DN of the user which wants to authenticate with the
    ldap_default_bind_dn and the password provided by the user.
    
    In order to do so, the least intrusive way is just by replacing
    sdap_connect*() functions by sdap_cli_connect*() functions in the LDAP's
    auth module.
    
    The simple change also allowed us to remove some code that is already
    executed as part of sdap_cli_connect*() and some functions had their
    names adapted to reflect better their new purpose.
    
    Resolves:
    https://pagure.io/SSSD/sssd/issue/3451
    
    Signed-off-by: Fabiano Fidêncio <fidencio@redhat.com>
    Reviewed-by: Sumit Bose <sbose@redhat.com>