Wenting Zheng

If Opaque's environment variables are not set, then the following error occurs: ```terminate called after throwing an instance of 'std::logic_error' what(): basic_string::_M_construct null not valid```. The Spark executor is also...

#153 upgrades Opaque to version 0.12.0, but anything beyond that seems to require changing the code in ServiceProvider.cpp because of a linking issue when mbedcrypto/mbedtls and oehostverify are both present.