too much warning for normal task routine

[maxshuang]

even for the normal task exit, we still find too much stack info for cancel

[2022/04/27 20:58:58.216 +08:00] [INFO] [worker.go:205] ["workerpool exited"] [worker-id=5acf7b46-5da9-474f-8850-2c3b2dd5f8c8] [error="context canceled"] [errorVerbose="context canceled\ngithub.com/pingcap/errors.AddStack\n\t/Users/maxshuang/go/pkg/mod/github.com/pingcap/errors@v0.11.5-0.20211224045212-9687c2b0f87c/errors.go:174\ngithub.com/pingcap/errors.Trace\n\t/Users/maxshuang/go/pkg/mod/github.com/pingcap/errors@v0.11.5-0.20211224045212-9687c2b0f87c/juju_adaptor.go:15\ngithub.com/pingcap/tiflow/pkg/workerpool.(*defaultAsyncPoolImpl).Run\n\t/Users/maxshuang/go/pkg/mod/github.com/pingcap/tiflow@v0.0.0-20220418100802-8c4f693f6456/pkg/workerpool/async_pool_impl.go:137\ngithub.com/hanfei1991/microcosm/lib.(*DefaultBaseWorker).doPreInit.func1\n\t/Users/maxshuang/GolandProjects/dataflow/microcosm/lib/worker.go:204\nruntime.goexit\n\t/opt/homebrew/Cellar/go/1.18/libexec/src/runtime/asm_arm64.s:1259"]
[2022/04/27 20:58:58.216 +08:00] [WARN] [center.go:37] ["More than one error is received"] [error="context canceled"] [errorVerbose="context canceled\ngithub.com/pingcap/errors.AddStack\n\t/Users/maxshuang/go/pkg/mod/github.com/pingcap/errors@v0.11.5-0.20211224045212-9687c2b0f87c/errors.go:174\ngithub.com/pingcap/errors.Trace\n\t/Users/maxshuang/go/pkg/mod/github.com/pingcap/errors@v0.11.5-0.20211224045212-9687c2b0f87c/juju_adaptor.go:15\ngithub.com/hanfei1991/microcosm/lib.(*DefaultBaseWorker).runHeartbeatWorker\n\t/Users/maxshuang/GolandProjects/dataflow/microcosm/lib/worker.go:420\ngithub.com/hanfei1991/microcosm/lib.(*DefaultBaseWorker).startBackgroundTasks.func1\n\t/Users/maxshuang/GolandProjects/dataflow/microcosm/lib/worker.go:401\nruntime.goexit\n\t/opt/homebrew/Cellar/go/1.18/libexec/src/runtime/asm_arm64.s:1259"]
[2022/04/27 20:58:58.216 +08:00] [INFO] [worker.go:205] ["workerpool exited"] [worker-id=18c7de6e-a4de-45a5-a1bb-e635a7b21169] [error="context canceled"] [errorVerbose="context canceled\ngithub.com/pingcap/errors.AddStack\n\t/Users/maxshuang/go/pkg/mod/github.com/pingcap/errors@v0.11.5-0.20211224045212-9687c2b0f87c/errors.go:174\ngithub.com/pingcap/errors.Trace\n\t/Users/maxshuang/go/pkg/mod/github.com/pingcap/errors@v0.11.5-0.20211224045212-9687c2b0f87c/juju_adaptor.go:15\ngithub.com/pingcap/tiflow/pkg/workerpool.(*defaultAsyncPoolImpl).Run\n\t/Users/maxshuang/go/pkg/mod/github.com/pingcap/tiflow@v0.0.0-20220418100802-8c4f693f6456/pkg/workerpool/async_pool_impl.go:137\ngithub.com/hanfei1991/microcosm/lib.(*DefaultBaseWorker).doPreInit.func1\n\t/Users/maxshuang/GolandProjects/dataflow/microcosm/lib/worker.go:204\nruntime.goexit\n\t/opt/homebrew/Cellar/go/1.18/libexec/src/runtime/asm_arm64.s:1259"]
[2022/04/27 20:58:58.216 +08:00] [WARN] [center.go:37] ["More than one error is received"] [error="context canceled"] [errorVerbose="context canceled\ngithub.com/pingcap/errors.AddStack\n\t/Users/maxshuang/go/pkg/mod/github.com/pingcap/errors@v0.11.5-0.20211224045212-9687c2b0f87c/errors.go:174\ngithub.com/pingcap/errors.Trace\n\t/Users/maxshuang/go/pkg/mod/github.com/pingcap/errors@v0.11.5-0.20211224045212-9687c2b0f87c/juju_adaptor.go:15\ngithub.com/hanfei1991/microcosm/lib.(*DefaultBaseWorker).runHeartbeatWorker\n\t/Users/maxshuang/GolandProjects/dataflow/microcosm/lib/worker.go:420\ngithub.com/hanfei1991/microcosm/lib.(*DefaultBaseWorker).startBackgroundTasks.func1\n\t/Users/maxshuang/GolandProjects/dataflow/microcosm/lib/worker.go:401\nruntime.goexit\n\t/opt/homebrew/Cellar/go/1.18/libexec/src/runtime/asm_arm64.s:1259"]