Run tests in parallel

[mikeharder]

• Only product change is using a unique temp dir for each invocation, which is a good thing for customers
• Test changes are just splitting code into 15 files, allowing "jest" to run them in parallel

Reduces test time on my dev machine from 74s to 15s. Build agent reduced less (71s to 39s) due to less CPU cores.

Dev Machine

Before

Test Suites: 2 passed, 2 total
Tests:       16 passed, 16 total
Snapshots:   0 total
Time:        73.946 s

After

Test Suites: 16 passed, 16 total
Tests:       16 passed, 16 total
Snapshots:   0 total
Time:        15.505 s

Build Agent

Before

Test Suites: 2 passed, 2 total
Tests:       16 passed, 16 total
Snapshots:   0 total
Time:        71.235 s

After

Test Suites: 16 passed, 16 total
Tests:       16 passed, 16 total
Snapshots:   0 total
Time:        38.918 s