openssl: Use separate DRBG for RNG_STRONG and RNG_TRUE with OpenSSL 1.1.1

openssl: Use separate DRBG for RNG_STRONG and RNG_TRUE with OpenSSL 1.1.1

OpenSSL 1.1.1 introduces DRGBs and provides two sources (same security
profile etc. but separate internal state), which allows us to use one for
RNG_WEAK (e.g. for nonces that are directly publicly visible) and the other
for stronger random data like keys.