Software install script fails if not enough cores on build machine

[rungitta]

15/53 Test #15: MdrunUtilityMpiUnitTests .....................***Failed    0.19 sec
--------------------------------------------------------------------------
There are not enough slots available in the system to satisfy the 4
slots that were requested by the application:  /tmp/centos/easybuild/build/GROMACS/2020.1/foss-2020a-Python-3.8.2/easybuild_obj/bin/mdrunutility-mpi-test

VM is used only had two cores. I guess it have to have at least four for this test to pass.

[boegel]

I guess we could check the value returned by nproc, or ask EasyBuild how many cores it thinks are available, and fail early if there are not enough.

Likewise for available memory, but it's harder to determine a correct lower limit there.
OpenFOAM is known to fail to build when there's only 16GB of RAM though...