Fix filestore peering network cleanup script

[tpdownes]

The filestore network peering script failed over the weekend due to an apparent parsing error. The solution worked for me locally before submitting, but I am providing what is likely a more portable fix by explicitly reading in a bash array using read -ra. The commenting is also improved to guide future developers understanding the solution.

Submission Checklist

• Have you installed and run this change against pre-commit? (pre-commit install)
• Are all tests passing? (make tests)
• Have you written unit tests to cover this change?
• Is unit test coverage still above 80%?
• Have you updated all applicable documentation?
• Have you followed the guidelines in our Contributing document?

[heyealex]

I tried out on my end, and everything seems to work as expected (at least locally). LGTM