Support Custom Engine

[heyuanliu-intel]

We want to use Intel QAT engine (https://github.com/intel/QAT_Engine) to accelerate the Java SSL/TLS processing.
But now wildfly openssl doesn't support custom engine.

And from the issue list of wildfly openssl, there is also other users need this feature.
wildfly-security/wildfly-openssl#76

[markwkern]

Should this work be done in wildfly-elytron? Seems like elytron might be far enough along, to avoid dual maintenance going forward.

[fjuma]

@markwkern This is the correct place for changes related to the WildFly OpenSSL Natives. The WildFly Elytron project doesn't include code related to WildFly OpenSSL.

@heyuanliu-intel Thanks very much for creating this issue and the PR! I've created a corresponding https://issues.redhat.com/browse/SSLNTV-29 JIRA issue to track this and will review the PR shortly. (We use the SSLNTV JIRA project for issue tracking but I just realized that information is currently missing in the REAMDE.md file, we'll update that soon.)

Apologies for the delayed response.