Print nicer error when failing to load project config

[bmonkman]

zero/internal/config/projectconfig/project_config.go

Lines 70 to 74 in 0c9bf0c

	log.Panicf("failed to read config: %v", err)
	}
	err = yaml.Unmarshal(data, &config)
	if err != nil {
	log.Panicf("failed to parse config: %v", err)

This is a fairly common failure case and it should be pretty obvious to the user how to resolve it, there's no need for the stack trace we get with log.Panicf, let's use exit.Fatal instead.