fix hbac rule search for non-admin users

hbacrule has it default attributes (which are used in search) attribute
'memberhostgroup'. This attr is not in ACI nor in schema. If the search
contains an attribute which can't be read then the search won't return
anything.

Therefore all searches with filter set fail.

https://fedorahosted.org/freeipa/ticket/5130

Reviewed-By: Martin Basti <mbasti@redhat.com>

ipalib/plugins/hbacrule.py

@@ -124,7 +124,7 @@ class hbacrule(LDAPObject):
         'description', 'usercategory', 'hostcategory',
         'servicecategory', 'ipaenabledflag',
         'memberuser', 'sourcehost', 'memberhost', 'memberservice',
-        'memberhostgroup', 'externalhost',
+        'externalhost',
     ]
     uuid_attribute = 'ipauniqueid'
     rdn_attribute = 'ipauniqueid'