fixed bug in ExecutionConfiguration
fixed bug in ExecutionConfiguration

The problem was that if using a CPU version of a ForceCompute in a GPU simulation, the simulation
crashed (e.g. in unit tests) due to not enough memory being allocated for all OMP threads

joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue