CMP0017: Fix check when including from CMake source tree

When running CMake from the build tree the CMAKE_ROOT is the
entire source tree.  Fix the CMP0017 check to be specific to
the Modules/ directory under CMAKE_ROOT so that Tests/ does
not count.  Fix the FindPackageTest modules to include FPHSA
by full path from CMAKE_ROOT so that they do not include the
local FPHSA which reports an error meant to test that CMP0017
works.
Merge topic 'fix-CMP0017-check' into next

7e187eea CMP0017: Fix check when including from CMake source tree