The retry when fetching containers from the registry didn't work because the
script was executed with `set -e`. Capture the error code also for non-zero
exit status.
Also use while loop instead of recursion and back off exponentially - start
with 5s and multiply by 3 (i.e. 5s, 15s, 45s - waiting in total up to 1 minute
for the registry to recover).
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