Display seconds since epoch using a more widely supported method

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What does this MR do?

Replaces $(date +%s) in the 'section start' and 'section end' output with $(awk 'BEGIN{srand(); print srand()}'). These are used to show the number of seconds since the epoch.

Why was this MR needed?

z/OS does not support the %s format for date.

What's the best way to test this MR?

Integration tests should catch this. This change was tested to be working on z/OS already.

What are the relevant issue numbers?