recipe/certificate_authority: use UTF-8 for CA certificate

The CertificateAuthority tool in ERP5 uses UTF8 encoding for certificates,
but by default OpenSSL does not. This cause an error when using non-ascii
characters:

```
The localityName field is different between CA certificate and the request
```

To solve the problem, the Certificate Authority recipe should use the same
encoding as ERP5, which requires adding `-utf8` option when invoking
OpenSSL.

For instance, creating a certificate with `localityName` Москва
will give the following with the default OpenSSL encoding:
`\C3\90\C2\9C\C3\90\C2\BE\C3\91\C2\81\C3\90\C2\BA\C3\90\C2\B2\C3\90\C2\B0`.

UTF8-encoding this same string gives `\D0\9C\D0\BE\D1\81\D0\BA\D0\B2\D0\B0`,
which is what ERP5 expects.