coverage: give the disconnect test something to disconnect

[martin-belanger]

The script disconnects a controller out from under stas and watches the daemon notice and reconnect. It had not done that in a long time: the phase before it sets "ip-family=ipv6", nvmet listened on 0.0.0.0, and 127.0.0.1 is the only address it answered on. So the one reachable controller was filtered out by address family, every other entry in that configuration is unreachable by design, and get_device() found nothing. Both halves printed "Failed to find a connection" in red and skipped, while the run still reported success.

nvmet listens on "::" instead. It accepts both families on the IPv6 wildcard but only IPv4 on the IPv4 one, so this is what the file's own commented-out alternative was for. The ipv6 phase now proves stas can connect over IPv6 rather than proving it cannot, which nothing else in the run covered.

That costs the one connection the target used to refuse, so a controller pointed at port 8010 takes its place. Nothing listens there, which is a sturdier way to be refused than a family mismatch, and it keeps ECONNREFUSED covered. It has to be an IPv6 address: this phase would filter out 127.0.0.1 before ever attempting to connect.

get_device() waits for a controller rather than sampling twice. One takes a moment to come up after a reload, and a parked discovery controller reports "nvme?" until its poll timer brings it back.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 69.11%. Comparing base (a16f9cc) to head (c2fd21c).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #514   +/-   ##
=======================================
  Coverage   69.11%   69.11%           
=======================================
  Files          16       16           
  Lines        2742     2742           
=======================================
  Hits         1895     1895           
  Misses        847      847           

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