Add `oscap` retries to `/per-rule`

[comps]

The problem is that oscap still crashes a lot, we see notable amounts of

oscap exited unexpectedly with 139    (segfault)

amongst the /per-rule results (when testing various rules), which typically dooms the entire /per-rule/*/$number run, and a re-run catches some other rule segfaulting.

So maybe check if oscap as a scanning (not remediating) command exited with non-0 and if it did, try running it again.

Do that in a for attempt in {1..5} bash loop, so that we give it a few tries.