Previously, etcd wrote to stderr in JSON format:

   {"level":"warn","ts":"2025-04-11T03:32:06.676527Z","caller":"embed/config.go:689","msg":"Running http and grpc server on single port. This is not recommended for production."}
   {"level":"warn","ts":"2025-04-11T03:32:06.676707Z","caller":"embed/config.go:689","msg":"Running http and grpc server on single port. This is not recommended for production."}
   {"level":"warn","ts":"2025-04-11T03:32:06.677056Z","caller":"etcdmain/etcd.go:146","msg":"failed to start etcd","error":"listen tcp 127.0.0.1:37803: bind: address already in use"}
   {"level":"fatal","ts":"2025-04-11T03:32:06.677104Z","caller":"etcdmain/etcd.go:204","msg":"discovery failed","error":"listen tcp 127.0.0.1:37803: bind: address already in use","stacktrace":"go.etcd.io/etcd/server/v3/etcdmain.startEtcdOrProxyV2\n\tgo.etcd.io/etcd/server/v3/etcdmain/etcd.go:204\ngo.etcd.io/etcd/server/v3/etcdmain.Main\n\tgo.etcd.io/etcd/server/v3/etcdmain/main.go:40\nmain.main\n\tgo.etcd.io/etcd/server/v3/main.go:31\nruntime.main\n\truntime/proc.go:272"}

This has several drawbacks:
- Not very readable.
- When used in tests which start etcd themselves (for example, scheduler_perf),
  the output is not associated with the current test.
- Contains warnings that are confusing for developers who don't know that they
  are harmless.

Intercepting output, parsing it and reformating makes the output nicer. Instead
of a mixture of JSON messages (see above) and normal test output, we now get
the etcd output embedded inside the test output. We can also filter out some
known harmless messages. Cleaning up more output or avoiding it in the first
place might be a good next step.

With `go test -v ./test/integration/scheduler_perf/dra`:

    === RUN   TestSchedulerPerf
    === RUN   TestSchedulerPerf/SchedulingWithResourceClaimTemplate
    === RUN   TestSchedulerPerf/SchedulingWithResourceClaimTemplate/fast
    I0411 13:21:03.353458   65212 feature_gate.go:385] feature gates: {map[SchedulerQueueingHints:false]}
    ...
    I0411 13:21:10.552975   65212 cidrallocator.go:210] stopping ServiceCIDR Allocator Controller
    I0411 13:21:10.567327   65212 etcd.go:210] "etcd output" logger="TestSchedulerPerf/SchedulingWithResourceClaimTemplate/fast" error="accept tcp 127.0.0.1:42245: use of closed network connection" level="warn" ts="2025-04-11T13:21:10.567045+0200" caller="embed/serve.go:160" msg="stopping insecure grpc server due to error"
    I0411 13:21:10.567398   65212 etcd.go:210] "etcd output" logger="TestSchedulerPerf/SchedulingWithResourceClaimTemplate/fast" ts="2025-04-11T13:21:10.567198+0200" caller="embed/serve.go:162" msg="stopped insecure grpc server due to error" error="accept tcp 127.0.0.1:42245: use of closed network connection" level="warn"
    I0411 13:21:15.567917   65212 etcd.go:227] "etcd didn't exit in 5 seconds, killing it" logger="TestSchedulerPerf/SchedulingWithResourceClaimTemplate/fast"
    I0411 13:21:15.567964   65212 etcd.go:234] "etcd exited" logger="TestSchedulerPerf/SchedulingWithResourceClaimTemplate/fast" err="signal: terminated"

With per-test output `go test -v ./test/integration/scheduler_perf/dra -args -use-testing-log`:

    === RUN   TestSchedulerPerf
    === RUN   TestSchedulerPerf/SchedulingWithResourceClaimTemplate
    === RUN   TestSchedulerPerf/SchedulingWithResourceClaimTemplate/fast
    I0411 13:19:03.540497   28645 feature_gate.go:385] feature gates: {map[DynamicResourceAllocation:true]}
    ...
    I0411 13:19:10.519994   28645 cidrallocator.go:210] stopping ServiceCIDR Allocator Controller
        etcd.go:210: I0411 13:19:10.533131] etcd output msg="stopping insecure grpc server due to error" error="accept tcp 127.0.0.1:46637: use of closed network connection" level="warn" ts="2025-04-11T13:19:10.532900+0200" caller="embed/serve.go:160"
        etcd.go:210: I0411 13:19:10.533274] etcd output msg="stopped insecure grpc server due to error" error="accept tcp 127.0.0.1:46637: use of closed network connection" level="warn" ts="2025-04-11T13:19:10.533022+0200" caller="embed/serve.go:162"
        etcd.go:227: I0411 13:19:15.533715] etcd didn't exit in 5 seconds, killing it
        etcd.go:234: I0411 13:19:15.533803] etcd exited err="signal: terminated"