@tonigi

I verified it, I will then modified a regtest so to keep checking for this

python module should always be called `plumed`, irrespectively of
prefix/suffix. Notice that if installing multiple plumed versions
side by side different python modules will anyway end up in different
directories (`lib/program_name`).

- tested for bias-exchange
- now new force-flags in gromacs so HREX should work equally to 2018
- ENERGY collective varialbe should be tested..

the new organisatoion of the gromacs source code allows simplifying
our patch. Multi-sim is now tested at least for multiple walkers
metad