Support older distros

[zmre]

Initial support will include distros that use openssl 1.0.2 and greater. Unfortunately, that means we will not support the following distros that only have openssl 1.0.1:

• Debian Jessie
• Debian Wheezy
• Ubuntu Trusty
• Ubuntu Precise
• Ubuntu Vivid
• CentOS 6

To manage this, we'll have to backport the OpenSSL AES keywrap functions and conditionally embed them into ironssh when the OpenSSL version is less than 1.0.2. Once backported, we'll need to add the mentioned distros to our build process and make sure they work.