Add global flags to set serial execution of python scripts

[sven-oly]

Each python function should have a way to turn off parallel processing.

Then, each top level script, e.g., generateDataAndRun.sh, may use a setting to control the use of multiprocessing.

[sffc]

I think this is a bandaid when we should be trying to find the root cause of the flakiness.

[sven-oly]

This is useful when debugging. Finally almost ready to go in each phase of the processing.
#430