schema: Add known_fingerprints option to schema command

When client requests schema it can list fingerprints of cached schemas
and server responds with SchemaUpToDate exception specifying fingeprint
of schema to use.

https://fedorahosted.org/freeipa/ticket/4739

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

ipaserver/plugins/schema.py

@@ -695,6 +695,13 @@ class output_find(BaseParamSearch):
 class schema(Command):
     NO_CLI = True
 
+    takes_options = (
+        Str(
+            'known_fingerprints*',
+            label=_("Fingerprint of schema cached by client")
+        ),
+    )
+
     @staticmethod
     def _calculate_fingerprint(data):
         """
@@ -748,4 +755,10 @@ class schema(Command):
         schema['fingerprint'] = schema_fp
         schema['ttl'] = SCHEMA_TTL
 
+        if schema['fingerprint'] in kwargs.get('known_fingerprints', []):
+            raise errors.SchemaUpToDate(
+                fingerprint=schema['fingerprint'],
+                ttl=schema['ttl'],
+            )
+
         return dict(result=schema)