functional-tester: refactor agent/tester

[gyuho]

Old functional-tester framework:

• Hard to extend when everything needs to be configured with flags
• Requires manual string parsing in agent side, which makes complicated implementation
• Hard to support more advanced agent operation (e.g. member reconfiguraton)
• Go standard rpc package is being deprecated

This PR refactors functional-tester code, both agent and tester:

• Typed RPC request/response to make it easier to extend
  • (Planned) support TLS
  • (Planned) membership reconfiguration
  • (Planned) failure-archive automatic uploads
  • (Planned) run failure injection testing with embedded etcd
• Remove all flags in agent and tester
• Keep one bi-directional stream between agent and tester (simpler)
• Better test data/agent server clean up on test completion
• Configure everything in YAML with more explicit field names
• Remove unused components (e.g. v2 stressers)

cd ${GOPATH}/src/github.com/coreos/etcd
./build

./tools/functional-tester/build

./bin/etcd-agent -h
./bin/etcd-tester -h
./bin/etcd-runner -h

rm -rf /tmp/etcd-agent-data*

./bin/etcd-agent --network tcp --address 127.0.0.1:19027
./bin/etcd-agent --network tcp --address 127.0.0.1:29027
./bin/etcd-agent --network tcp --address 127.0.0.1:39027

./bin/etcd-tester --config ./tools/functional-tester/tester/local-test.yaml

make pull-docker-functional-tester -f ./hack/scripts-dev/Makefile
cd ./tools/functional-tester

# run 3 agents for 3-node local etcd cluster
./scripts/docker-local-agent.sh 1
./scripts/docker-local-agent.sh 2
./scripts/docker-local-agent.sh 3

./scripts/docker-local-tester.sh

Doesn't change any agent/tester(stresser) logic.
Preliminary work to support TLS tests #8943.

[codecov-io]

Codecov Report

Merging #9513 into master will decrease coverage by 0.11%.
The diff coverage is 62.01%.

@@            Coverage Diff             @@
##           master    #9513      +/-   ##
==========================================
- Coverage    72.5%   72.39%   -0.12%     
==========================================
  Files         366      366              
  Lines       31000    31128     +128     
==========================================
+ Hits        22476    22534      +58     
- Misses       6891     6969      +78     
+ Partials     1633     1625       -8

Impacted Files	Coverage Δ
pkg/transport/proxy.go	59.15% <62.01%> (+1.36%)	⬆️
client/client.go	57.84% <0%> (-26.8%)	⬇️
etcdctl/ctlv3/command/auth_command.go	59.09% <0%> (-11.37%)	⬇️
proxy/grpcproxy/register.go	80.55% <0%> (-2.78%)	⬇️
etcdserver/api/v3election/election.go	66.66% <0%> (-2.78%)	⬇️
proxy/grpcproxy/lease.go	78.28% <0%> (-2.27%)	⬇️
proxy/grpcproxy/watch.go	86.33% <0%> (-1.25%)	⬇️
etcdserver/v3_server.go	79.17% <0%> (-0.78%)	⬇️
clientv3/watch.go	95.34% <0%> (-0.5%)	⬇️
clientv3/balancer/grpc1.7-health.go	86.33% <0%> (ø)	⬆️
... and 16 more

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