Set PARALLEL_TEST environment variable.
PARALLEL_TEST → PARALLEL_TESTS
Try to set PARALLEL_TESTS to number of processes.
Add specs.
Get rid of comments per PR feedback.
Pass num_processes all the way through to execute_command() so PARALLEL_TESTS can be set to it.
PARALLEL_TESTS → PARALLEL_TEST_GROUPS
Merge pull request #172 from jshraibman-mdsol/feature/env_var

Set PARALLEL_TEST environment variable.