[dv regr tool] Use builtin for generating seeds
[dv regr tool] Use builtin for generating seeds

- The tool used octal dump [`od`] to pre-populate a list of 1000 random
numbers to be supplied as seeds to the tests
- Due to an unknown issue this ended up hanging on WDC machines
- This PR changes it to use python3 in-built library called 'secrets'
instead, which supposedly produces strong random numbers suitable for
crypto applications.
- Performance wise, the secrets lib takes 0.005s to generate 1000 random
numbers which is an order of magniture better than `od` which is a
system call that takes 0.097s. So this is an added plus.

Signed-off-by: Srikrishna Iyer <2803d640feace36379942447842f26c7747b4dc3@google.com>

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