Dear Joseph, the package you have to install is called "openssl-devel" (at least on CentOS 7.2). This package has to be present in your image. The error message you're getting tells you that easybuild cannot find that package in your image.
When, in your image, you look at the output of the command
yum info openssl-devel
you should see
Repo : installed
If you don't see that, you need to change your image until the "yum
info" shows the package as installed.
Sunny greetings,
Andreas
