keyring_vault timeout MTR tests always producing warnings

keyring_vault.timeout_basic              w2 [ fail ]  Found warnings/errors in server log file!
        Test ended at 2018-01-22 16:46:54
line
2018-01-22T21:46:54.258844Z 0 [ERROR] Plugin keyring_vault reported: 'File '' not found (Errcode: 2 - No such file or directory)'
^ Found warnings in /mnt/workspace/percona-server-5.7-trunk/BUILD_TYPE/release/Host/ubuntu-trusty-64bit/build/mysql-test/var/2/log/mysqld.1.err
ok

keyring_vault.keyring_vault_timeout      w2 [ fail ]
        Test ended at 2018-01-22 16:47:38

CURRENT_TEST: keyring_vault.keyring_vault_timeout
--- /mnt/workspace/percona-server-5.7-trunk/BUILD_TYPE/release/Host/ubuntu-trusty-64bit/plugin/keyring_vault/tests/mtr/keyring_vault_timeout.result	2018-01-22 23:14:42.397648000 +0300
+++ /mnt/workspace/percona-server-5.7-trunk/BUILD_TYPE/release/Host/ubuntu-trusty-64bit/build/mysql-test/var/2/log/keyring_vault_timeout.reject	2018-01-23 00:47:38.096652342 +0300
@@ -5,6 +5,9 @@
 call mtr.add_suppression("\\[ERROR\\] Plugin keyring_vault reported: 'Error while loading keyring content. The keyring might be malformed'");
 call mtr.add_suppression("\\[ERROR\\] Plugin keyring_vault reported: 'CURL returned this error code: 28 with error message : connect\\(\\) timed out!'");
 INSTALL PLUGIN keyring_vault SONAME 'keyring_vault.so';
+Warnings:
+Warning	29	File '' not found (Errcode: 2 - No such file or directory)
+Warning	42000	keyring_vault initialization failure. Please check the server log.
 include/assert.inc [Default vaule of keyring_vault_timeout should be 15]
 SET @@GLOBAL.keyring_vault_timeout=15;
 SET @@GLOBAL.keyring_vault_config='MYSQLTEST_VARDIR/std_data/keyring_vault_confs/keyring_vault_incorrect_server.conf';

mysqltest: Result content mismatch