Ensure init is idempotent and doesn't overwrite repo list.

[calebbrown]

When a pod is restarted an initContainer can be run again.

The documentation says:

Because init containers can be restarted, retried, or re-executed, init container code should be idempotent. In particular, code that writes to files on EmptyDirs should be prepared for the possibility that an output file already exists.

This PR ensures that the collect_signals init script is idempotent so that the pod can be safely restarted.