Ftr: Gracefully shutdown

[flycash]

What this PR does:
Gracefully shutdown. The steps are:

1. Destroy all registries;
2. wait for the new request for a short time
3. provider rejects new request and then wait for processing all requests;
4. consumer rejects sending new request and then wait for response
5. invoke custome shutdown callback
   Which issue(s) this PR fixes:

Fixes #239

Special notes for your reviewer:

Please check the order of releasing resources.

Does this PR introduce a user-facing change?:

Now the application can shutdown gracefully

[flycash]

It seems that the syscall.SIGEMT cannot be found in CI.

[flycash]

I'm sorry that I had merge master and bring its change list into this PR

[codecov-io]

Codecov Report

Merging #255 into develop will decrease coverage by 0.79%.
The diff coverage is 70.21%.

@@            Coverage Diff             @@
##           develop     #255     +/-   ##
==========================================
- Coverage    66.24%   65.45%   -0.8%     
==========================================
  Files          108      111      +3     
  Lines         6903     7043    +140     
==========================================
+ Hits          4573     4610     +37     
- Misses        1879     1978     +99     
- Partials       451      455      +4

Impacted Files	Coverage Δ
remoting/etcdv3/facade.go	0% <ø> (ø)	⬆️
remoting/etcdv3/listener.go	46.08% <ø> (ø)	⬆️
registry/etcdv3/listener.go	76.74% <ø> (ø)	⬆️
remoting/etcdv3/client.go	57.8% <ø> (ø)	⬆️
config/consumer_config.go	59.25% <ø> (ø)	⬆️
registry/etcdv3/registry.go	51.51% <ø> (ø)	⬆️
config/provider_config.go	58.53% <ø> (ø)	⬆️
registry/nacos/listener.go	80% <ø> (ø)	⬆️
registry/nacos/registry.go	61.78% <ø> (ø)	⬆️
registry/zookeeper/listener.go	61.7% <0%> (ø)	⬆️
... and 14 more

---

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[flycash]

All comments had been fixed and I've tested it end to end again.

[fangyincheng]

LGTM

[AlexStocks]

LGTM

[hxmhlt]

LGTM

[pantianying]

LGTM