add a parameter for nthreads

from mantid import config

config['Q.convention'] = "Crystallography"

DownloadInstrument(ForceUpdate=True)

config['MultiThreaded.MaxCores'] == 1

os.environ['OPENBLAS_NUM_THREADS'] = '1'

os.environ['OMP_NUM_THREADS'] = '1'

os.environ['_SC_NPROCESSORS_ONLN'] = '1'

nthreads = os.environ.get('TOPAZ_NUM_THREADS', '1')

config['MultiThreaded.MaxCores'] == int(nthreads)

os.environ['OPENBLAS_NUM_THREADS'] = nthreads

os.environ['OMP_NUM_THREADS'] = nthreads

os.environ['_SC_NPROCESSORS_ONLN'] = nthreads

import numpy as np

import itertools