Publish the most recent CTP7 Linux image

Description

If the CTP7 Linux image hasn't changed in years, some work was invested to build additional libraries and tools, in particular the perf profiler.

One could also consider updating the dependencies (matching the CentOS 7 versions?) as compile log4cplus with C++11 support.

Possible fixes

Publish the Linux image to the cmsgemos website, use it in the CI, and deploy it wherever needed. Ideally, the build instructions should be provided in a Git repository (this one?)