FlakyTest by flaky findAddress() helper - TestServerShutdownHTTP

[szuecs]

See first log message bind: address already in use, but we just before tested that we can use the port. Either Close() did not work correctly (maybe handle error in l.Close() and retry on error) or some other test found the same port and used it (may need a global lock and a global test package to have a global helper func for tests).

ok  	github.com/zalando/skipper/rfc	0.002s
time="2023-11-06T11:20:53Z" level=error msg="Failed support listener: listen tcp 0.0.0.0:46473: bind: address already in use"
time="2023-11-06T11:20:53Z" level=info msg="starting polling" timeout=500ms
time="2023-11-06T11:20:53Z" level=info msg="routes initialized" bytes=400 count=3 etag="\"916d970716e7669c04dd11b6d6828af03ecc209ed014eb41fc2bf010e0a1c282\""
time="2023-11-06T11:20:53Z" level=info msg="routes updated" bytes=400 count=3 etag="\"916d970716e7669c04dd11b6d6828af03ecc209ed014eb41fc2bf010e0a1c282\""
--- FAIL: TestServerShutdownHTTP (1.07s)
    shutdown_test.go:91: kube endpoint: "http://127.0.0.1:37015"
    shutdown_test.go:93: test endpoint: "http://[::]:46473/routes"
    shutdown_test.go:93: test endpoint: "http://[::]:46473/metrics"
    shutdown_test.go:147: Failed to get failed to get expected status code 200 for "http://[::]:46473/metrics", got: 404