Merge branch 'fixes-to-cmake-modules' into 'master'

Fixes to CMake modules

- improved inherited heptools version lookup
- fixed backward compatibility issue
- fixed GAUDI-1299 (fix ignore of subdirectories if binary tag contains `+`)
- fixed issue with data package lookup for versions without digits
- fixed content of `manifest.xml` for special platform `*-do0`
- protected AFS workaround to avoid problems with CMVFS
- improve relocatability of compiler path (via `LCG_releases_base` env var)
- removed a few hacks for old versions of gcc
- enable c++17 for gcc >= 7

See merge request !312