cpack was used to get the list of available i.e. ACTIVE CPack generators
in the CMake tests suite. This was done in order to get dynamically
available CPack generators like DEB or RPM that may or may not be
available on some platform like MacOSX depending on the fact that
some command are installed or not. We may do that but not during
initial configuration.
The current patch fixes the problem and we may do better in the future
like configuring CPack tests later.