[CashTab] Only show console messages if test fails
Adds a script to show console messages only if the tests fails. Currently when running our tests, there is a lot of noise from console even if everything is fine and the test passes.
Also adds CI=true flag to npm run test:coverage script, thus making watchMode false. This is required for further CI usage.
Test Plan: npm install && npm run test:coverage. Should not show any console messages unless a test fails. Should also not be in watchMode.
Reviewers: #bitcoin_abc, majcosta
Reviewed By: #bitcoin_abc, majcosta
Differential Revision: https://reviews.bitcoinabc.org/D8608