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##### SUMMARY
Allow to specify a new "format" parameter in "openssl_privatekey". Today the output format is decided by a very simple heuristic which requires further commands to work properly.
I need, for example, to generate a RSA private key but in PKCS8 format. The current heuristic uses OpenSSH format for RSA keys and only uses PKCS8 for Ed25519 and similar. This makes me use a "command" with "openssl" to convert the generated key, which leads to idempotency problems and unnecessary complexity.

##### ISSUE TYPE
- Feature Idea

##### COMPONENT NAME
openssl_privatekey

##### ADDITIONAL INFORMATION
<!--- Describe how the feature would be used, why it is needed and what it would solve -->
The current heuristic should be kept unless overwritten by user.

<!--- Paste example playbooks or commands between quotes below -->
```yaml
openssl_privatekey:
  path: /etc/ssl/private/ansible.com.pem
  format: pkcs8
```
The values allowed are `pkcs1`, `raw` and `pkcs8`

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return crypto_utils.get_fingerprint(self.path, self.passphrase)
    def _check_passphrase(self):
        try:
            crypto_utils.load_privatekey(self.path, self.passphrase)
            return True
        except Exception as dummy:
            return False
    def _check_size_and_type(self):
        def _check_size(privatekey):
            return self.size == privatekey.bits()
        def _check_type(privatekey):
            return self.type == privatekey.type()
        try:
            privatekey = crypto_utils.load_privatekey(self.path, self.passphrase)
        except crypto_utils.OpenSSLBadPassphraseError as exc:
            raise PrivateKeyError(exc)
        return _check_size(privatekey) and _check_type(privatekey)
    def dump(self):
        """Serialize the object into a dictionary."""
        result = super(PrivateKeyPyOpenSSL, self).dump()
        if self.type == crypto.TYPE_RSA:
            result['type'] = 'RSA'
        else:
            result['type'] = 'DSA'
        return result
class PrivateKeyCryptography(PrivateKeyBase):