The entrypoint package wraps the step commands and execute them. This
allows use to use pods containers with some order. In a step, the
entrypoint binary will wait for the file of the previous step to be
present to execute the actual command.
Before this change, if a command failed (`exit 1` or something),
entrypoint would not write a file, and thus the whole pod would be
stuck running (all the next step would wait forever).
This fixes that by always writing the post-file — and making
the *waiter* a bit smarter :
- it will now look for a `{postfile}.err` to detect if the previous
step failed or not.
- if the previous steps failed, it will fail too without executing the
step commands.
Signed-off-by: Vincent Demeester <vdemeest@redhat.com>