Include OPENSSL_DIR

[uilianries]

Hi!

OpenSSL is a requirement for Macchina.io and there is no package manager to solve it. So, we need to make sure that openssl libraries and headers are available in the path, before to build.

I saw the variable OPENSSL_DIR here. We could use this variable same for all system, as an argument:

$ make DEFAULT_TARGET=shared_release OPENSSL_DIR=/opt/openssl

Regards.