Livy Interpreter support two way SSL

Our Livy instance is behind a reverse proxy that protects Livy with two way SSL (also known as client side SSL or mutual SSL authentication). To support this, the http client in the Livy interpreter should be extended to also receive "key material" e.g.:

SSLContext sslContext = SSLContexts.custom()
     .loadKeyMaterial(keyStore, password)
     .loadTrustMaterial(trustStore) 
     .build(); 

Naturally, adding the keyStore should only be done if a relevant keystore property (to be added with this Jira as well) is not blank.