storage: Cast CSR identifiers into strings.

While identifiers are integers, they could just as well be treated as
opaque identifiers by external applications.

caucase/cli.py

@@ -211,7 +211,7 @@ class CLICaucaseClient(object):
     )
     for entry in self._client.getPendingCertificateRequestList():
       csr = utils.load_certificate_request(entry['csr'])
-      print '%20i | %r' % (
+      print '%20s | %r' % (
         entry['id'],
         csr.subject,
       )

caucase/storage.py

@@ -322,7 +322,7 @@ class SQLite3Storage(local):
     with self._db as db:
       return [
         {
-          'id': x['id'],
+          'id': str(x['id']),
           'csr': x['csr'].encode('ascii'),
         }
         for x in db.cursor().execute(