IPA_RULES_COMMON: Introduce ipa_common_save_rules()
    
    This method is kind of a replacement for ipa_save_hbac() one.
    
    While ipa_save_hbac() wasn't removed, its porpuse has been totally
    changed. Now it just prepare the ground and calls
    ipa_common_save_rules() which is a more generic function that can be
    reused for new backend modules.
    
    In order to make the code cleaner a new structure has also been
    introduced: struct ipa_common_entries; which contains the values that
    will be used to save the entry and the entrygroup to sysdb.
    
    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>