fix(config): Separate ENOENT error handler from others

This prevents karma from incorrectly reporting a config file not found error in the case where the code inside the config file throws an ENOENT error for other reasons

style(config): indentation, error messages

Fix indentation mistake, improve error message, add process.exit(1)

test(config): add missing test

to ensure proper error reporting when a config file throws an ENOENT error of its own

style(config): whitespace and var scope

Removed trailing whitespace and moved configSrc declaration outside of the try/catch block