fix(launcher): Debug Child Processes exit signal (#3259)
fix(launcher): Debug Child Processes exit signal (#3259)

The Child Processes Event: 'exit' has two parameters: code and signal
(https://nodejs.org/api/child_process.html#child_process_event_exit).
One of the two will always be non-null. This helps debugging cases where
code is null.
david-garcia-nete/karma,maksimr/karma,karma-runner/karma,karma-runner/karma,david-garcia-nete/karma,johnjbarton/karma,karma-runner/karma,johnjbarton/karma,johnjbarton/karma,david-garcia-nete/karma,maksimr/karma,karma-runner/karma,johnjbarton/karma,maksimr/karma