[FIX] models: Escape `%` characters from error messages of a failed import

To prevent susbtituion exception when creating use error message
e.g. No matching record found for external id 'fo%o' in field 'Bar'
Fixes #5933

openerp/models.py

@@ -1199,8 +1199,11 @@ class BaseModel(object):
             type = 'warning' if isinstance(exception, Warning) else 'error'
             # logs the logical (not human-readable) field name for automated
             # processing of response, but injects human readable in message
-            record = dict(base, type=type, field=field,
-                          message=unicode(exception.args[0]) % base)
+            # Before applying string substitution, we need to escape all '%'
+            # characters that are not part of substitutable reference.
+            regex = '%%(?!\((%s)\)s)' % '|'.join(base.keys())
+            message = unicode(re.sub(regex, '%%', exception.args[0])) % base
+            record = dict(base, type=type, field=field, message=message)
             if len(exception.args) > 1 and exception.args[1]:
                 record.update(exception.args[1])
             log(record)