Avoid acceptance test port conflicts

[teor2345]

Motivation

Windows can reserve or use ports up to 53500.

Windows and macOS sequentially allocate ephemeral ports, starting at 41952.

See the code comment for the full details.

Solution

Start Zebra's random acceptance test ports at 53500.

Review

@oxarbitrage has also looked at this issue. It's urgent, because it's causing CI failures.

Related Issues

Closes #1769
Closes #1765

Follow Up Work

If these issues continue, we should:

• ask the OS to allocate a listener port, by configuring port 0
• read the actual port from zebrad's logs
• launch the test or conflicting process with that port

This is now ticket #1813.

[teor2345]

I want to auto-merge this after all the tests have passed, but GitHub doesn't give me that option.

[oxarbitrage]

Looks good, i never checked if when this fails we were below port 53500 but by the links makes sense to start there. Lets try it.

[teor2345]

Looks good, i never checked if when this fails we were below port 53500 but by the links makes sense to start there. Lets try it.

Check out the newer logs in #1769:

Opening metrics endpoint listener 127.0.0.1:49821 failed

When I saw that I thought: "weird, that's really close to 49152" (the start of the range).

Before #1766 and #1770, zebrad and the tests didn't show these ports, so the issue was a lot harder to diagnose.