test(firecracker): derive netpool names from config, not hardcoded defaults

The KVM CI runner now sets BOT_BOTTLE_FC_* for its isolated pool (distinct
iface prefix / orch iface / nft table / IP base), and that env leaks into the
coverage job's test process. Five netpool tests hardcoded the default names
(bbfc*, bot_bottle_fc) and so failed there with e.g. ['bbfc1'] != ['bbci1'].

Assert against netpool's env-driven config instead — slot(i).iface / the
configured prefix — so the tests check the LOGIC regardless of which pool the
host is configured for. The single-source test now compares the parsed
defaults (netpool._DEFAULTS, env-independent) for the module constants, since
IFACE_PREFIX/NFT_TABLE legitimately layer an env override on top.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01A9qa3xoavjQScufDfZaXKR

tests/unit/test_firecracker_helpers.py

@@ -63,9 +63,12 @@ class TestNetpoolProbes(unittest.TestCase):
         self.assertEqual(2, ok.call_count)
 
     def test_missing_taps(self):
+        # Derive the expected iface from netpool's (env-driven) config rather
+        # than hardcoding "bbfc1": the KVM CI runner sets BOT_BOTTLE_FC_* for
+        # its isolated pool, so the prefix there is not the default.
         with patch.dict("os.environ", {"BOT_BOTTLE_FC_POOL_SIZE": "2"}), \
              patch.object(netpool, "tap_present", side_effect=[True, False]):
-            self.assertEqual(["bbfc1"], netpool.missing_taps())
+            self.assertEqual([netpool.slot(1).iface], netpool.missing_taps())
 
     def test_orch_slot_is_top_of_ip_base_16(self):
         # Dedicated orchestrator link: /31 at the top of the IP_BASE /16,