Certificate search max_serial_number problem fixed

Maximum serial number field now accepts only positive numbers

https://fedorahosted.org/freeipa/ticket/4163

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

ipalib/plugins/cert.py

@@ -650,10 +650,12 @@ class cert_find(Command):
             doc=_("minimum serial number"),
             autofill=False,
             minvalue=0,
+            maxvalue=2147483647,
         ),
         Int('max_serial_number?',
             doc=_("maximum serial number"),
             autofill=False,
+            minvalue=0,
             maxvalue=2147483647,
         ),
         Flag('exactly?',