ref(docker): combine test and prod entrypoints into one

This makes the following changes
- Uses `-x` instead of echoing the variables values
- Sets default values where required
- Create a function to list directories
- Create a function to run cargo tests
- Use a better approach to handle different options in the `case` manegement for tests and production
- Replaces all instances of `runtime-entrypoint.sh` with `entrypoint.sh`

.dockerignore

@@ -21,4 +21,3 @@
 !zebra-*
 !zebrad
 !docker/entrypoint.sh
-!docker/runtime-entrypoint.sh