ARSN-84 Correct Jest configuration for test suites and coverage
ARSN-84 Correct Jest configuration for test suites and coverage

Thanks to files renaming, we can follow as much as we can the jest
default configurations. The options are gone, and we're specifying only
the maxWorkers (because the test suite is linear, and bugs if we're
running it in parallel) and the collect coverage files.
The coverage script itself is joined into one command instead of three
to leverage the Jest builtin coverage.

scality/Arsenal,scality/Arsenal