IPA_ACCESS: Make ipa_purge_hbac() more generic
    
    This mothod can also be reused in the future for new backend modules.
    
    In order to make it more generic, let's just move it to
    ipa_rules_common.[ch], rename it to ipa_common_purge_rules() and make
    the subtreename to be purged a new paramether of this method.
    
    Related:
    https://pagure.io/SSSD/sssd/issue/2995
    
    Signed-off-by: Fabiano Fidêncio <fidencio@redhat.com>
    
    Reviewed-by: Pavel Březina <pbrezina@redhat.com>
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>