schema: Introduce schema cache format

Information about schema cache format is stored in every cache item.
When schema cache format changes in incompatible way format will be
increased. When format stored in cache doesn't match currently used
format the entry in cache is ignored.

https://fedorahosted.org/freeipa/ticket/6048

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

ipaclient/remote_plugins/schema.py

@@ -23,6 +23,8 @@ from ipapython.dn import DN
 from ipapython.dnsutil import DNSName
 from ipapython.ipa_log_manager import log_mgr
 
+FORMAT = '0'
+
 if six.PY3:
     unicode = str
 
@@ -478,6 +480,14 @@ class Schema(object):
         return _LockedZipFile(path, mode)
 
     def _get_schema_fingerprint(self, schema):
+        try:
+            fmt = json.loads(schema.read('format'))
+        except KeyError:
+            fmt = '0'
+
+        if fmt != FORMAT:
+            raise RuntimeError('invalid format')
+
         schema_info = json.loads(schema.read(self.schema_info_path))
         return schema_info['fingerprint']