Testing/forces update

[shuds13]

Update forces tests.

For relevant forces tests

• Use persistent generator as default
• Use new OO interface

Other capabilities

• Add generator that sets num_gpus based on x value in range(e.g. number of particles)
• Update regression test test_GPU_variable_resources.py to use new gen (as well as old).

Tests

• Updating forces_simple and forces_gpu and prob. forces_multi_task/
• Remove forces_gpu_persis_gen - as now that's default
• Add a var resources test (separate now - and using new num_gpus generator)

Update tutorials

• Forces simple
• Forces GPU

[jlnav]

You could use ensemble.persis_info = add_unique_random_streams({}, ensemble.nworkers + 1) if you think its more clear

[shuds13]

Good point. I'm realising it means an extra import (from tools) which is a pain.

[jlnav]

Yeah. That's one of the reasons I made Ensemble.add_random_streams() originally, I think I forgot to mention. Avoid an import, keep it simple for 75% of our tests

[jlnav]

Looks good!