(#21029) 3.x masters require OpenSSL 0.9.8o+

In 3.x, the default digest algorithm for the CA certificate was upgraded to
SHA256 from SHA1. Agents communicating with 3.x masters will need OpenSSL 0.9.8x
or newer.
Merge pull request #174 from Sharpie/21029-update-ssl-requirements

(#21029) 3.x masters require OpenSSL 0.9.8o+