ipatests: fix get_user_result method
Because the sidgen plugin is a postop plugin, it is not
always triggered before the result of an ADD is returned
and the objectclasses of the user may / may not contain
ipantuserattrs.
Fix the get_user_result method to work in all the cases.
Related: https://pagure.io/freeipa/issue/8995
Signed-off-by: Florence Blanc-Renaud <flo@redhat.com>
Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>