Fix selfservice-find crashes

Ignore empty options when performing an ACI search so that the
find command does not crash. Update ipa(1) man page to mention
this common behavior of find commands.

https://fedorahosted.org/freeipa/ticket/2011
https://fedorahosted.org/freeipa/ticket/2012

tests/test_xmlrpc/test_selfservice_plugin.py

@@ -153,6 +153,25 @@ class test_selfservice(Declarative):
         ),
 
 
+        dict(
+            desc='Search for %r with empty attrs and permissions' % selfservice1,
+            command=('selfservice_find', [selfservice1], {'attrs' : None, 'permissions' : None}),
+            expected=dict(
+                count=1,
+                truncated=False,
+                summary=u'1 selfservice matched',
+                result=[
+                    {
+                        'attrs': [u'street', u'c', u'l', u'st', u'postalcode'],
+                        'permissions': [u'write'],
+                        'selfaci': True,
+                        'aciname': selfservice1,
+                    },
+                ],
+            ),
+        ),
+
+
         dict(
             desc='Update %r' % selfservice1,
             command=(