print warning log when virtual service config error

[wulianglongrd]

These scenarios are matching conflicts or configuration errors and cannot be detected by webhooks. It makes sense to change to printing warning logs so that we can detect problems through logs in time when applying configuration, because we do not enable debug logs by default.

[zirain]

cc @ericvn macbuildcheck_istio stuck

[hanxiaop]

/retest

[ericvn]

cc @ericvn macbuildcheck_istio stuck

Must have been a flake:

GOOS=darwin GOARCH=amd64 LDFLAGS='-extldflags -static -s -w' common/scripts/gobuild.sh /home/prow/go/src/istio.io/istio/out/linux_amd64/ -tags=agent,disable_pgv ./pilot/cmd/pilot-agent
# istio.io/istio/pkg/config/schema/collections
pkg/config/schema/collections/collections.agent.gen.go:280:11: undefined: EnvoyFilter
pkg/config/schema/collections/collections.agent.gen.go:304:11: undefined: EnvoyFilter
pkg/config/schema/collections/collections.agent.gen.go:322:12: undefined: EnvoyFilter
pkg/config/schema/collections/collections.agent.gen.go:340:13: undefined: EnvoyFilter

I'll keep an eye on the test. So far only this one failure.

[hzxuzhonghu]

Previously we use debug on purpose to reduce spammy logs during xds push. And we expect user to use istioctl analysis.

[wulianglongrd]

/retest