NEST package update

These changes add the nest@3.2 release to the Spack package and some flag processing changes. Most notably the boost variant was added and activated by default. This is most likely wanted, since with boost sorting algorithms some NEST versions can be orders of magnitude faster.

merged

mentioned in commit 2e842fb9

Hi @terhorst ,

I modified also spack.yaml to let nest@3.2 build.
It seems that the build process has completed successfully (here).

Please check and validate the installation in lab-int.

Best