baseldap: Handle missing parent objects properly in *-find commands

The find_entries function in ipaldap does not differentiate between
a LDAP search that returns error code 32 (No such object) and LDAP
search returning error code 0 (Success), but returning no results.

In both cases errors.NotFound is raised. In turn, LDAPSearch
commands interpret NotFound exception as no results.

To differentiate between the cases, a new error EmptyResult
was added, which inherits from NotFound to preserve the compatibility
with the new code.

This error is raised by ipaldap.find_entries in case it is performing
a search with and the target dn does not exist.

https://fedorahosted.org/freeipa/ticket/4659

Reviewed-By: Jan Cholasta <jcholast@redhat.com>

ipapython/ipaldap.py

@@ -1527,7 +1527,7 @@ class LDAPClient(object):
                     break
 
         if not res and not truncated:
-            raise errors.NotFound(reason='no such entry')
+            raise errors.EmptyResult(reason='no matching entry found')
 
         return (res, truncated)