(tests) Make it easier to change # of cores in matmul.
(tests) Make it easier to change # of cores in matmul.

nkawahara/Graphite,victorisildur/Graphite,8l/Graphite,victorisildur/Graphite,mit-carbon/Graphite-Cycle-Level,mit-carbon/Graphite,mit-carbon/Graphite,mit-carbon/Graphite,fhijaz/Graphite,victorisildur/Graphite,victorisildur/Graphite,mit-carbon/Graphite-Cycle-Level,mit-carbon/Graphite,fhijaz/Graphite,fhijaz/Graphite,8l/Graphite,mit-carbon/Graphite-Cycle-Level,8l/Graphite,nkawahara/Graphite,8l/Graphite,nkawahara/Graphite,nkawahara/Graphite,fhijaz/Graphite,mit-carbon/Graphite-Cycle-Level