Session reuse required

When connecting with SSL and set `require_ssl_reuse=YES` at vsftpd.conf, I got following message.
And plugin could upload file but remote file became 0 byte.

```
DEBUG: Client "xx.xxx.xxx.xxx", "Connection terminated without SSL shutdown - buggy client?"
```

While plugin was retrying, following message was shown.

```
FTP put request failed. Retrying 6/10 after 16 seconds. Message: SSL connection failed; session reuse required: see require_ssl_reuse option in vsftpd.conf man page
```
### Reproducible conditions
#### Server side
- vsftpd v2.2.2.
- set `require_ssl_reuse=YES` at vsftpd.conf
#### Client side
- embulk-output-ftp v0.1.5

Start by reproducing embulk-output-ftp v0.1.5 against vsftpd v2.2.2 with require_ssl_reuse=YES, using the reported FTP upload and retry messages as the baseline. Investigate the plugin's SSL connection handling; done means uploads complete successfully without zero-byte remote files or session-reuse failures.

Written by the indexing model from the issue text.