Support PKCS#11 keystores

[wsargent]

Should be possible to use ssl-config with an HSM solution such as CloudHSM or YubikeyHSM, using the PKCS#11 module:

https://docs.oracle.com/javase/8/docs/technotes/guides/security/p11guide.html#Login

char[] pin = ...; 
KeyStore ks = KeyStore.getInstance("PKCS11");
ks.load(null, pin); char[] pin = ...;  KeyStore ks = KeyStore.getInstance("PKCS11"); ks.load(null, pin);