build is hanging if there is launcher initialization error

[jithine]

What happened:

Launcher is exiting with 0 status code even when it errors out. This causes a problem that errors in initialization is not caught and build hangs for ever.

What you expected to happen:

1. launcher should exit non-zero on initialization errors
2. Screwdriver should detect such errors during a build's initialization and mark the build as failure.

How to reproduce it:

1. Start a build with ubuntu:18.04 container
2. Build hangs in UI. k8s container exited with Completed state.

[jithine]

Launch to always exit 0 change was introduced in this PR many years ago. But we seem to have overused it by taking the same logic even before a build actually starts running