Integration tests make target

Integration tests executable using 'make integration_tests'. Clean up CI
a bit.

Change log:
* add integration_tests as a CMake target
* use integration_tests make target in CI
* update README
* CMake command compatible with CentOS7
* CI adjustments
6 jobs for 112-integration-tests-as-a-cmake-target in 13 minutes and 49 seconds (queued for 1 second)