etcd_docker 3: Incorporate docker based etcd integration package into… (#4147)

* etcd_docker 2: Add a docker based etcdintegration package

PR 2 for #4144

High level approach is as described in #4144 . This PR adds:

- Functions to spin up a 1 node etcd cluster using docker (in `dockerexternal`)
- A drop in replacement for the etcd/integration package using `dockerexternal`

commit-id:e4e80f1d

* etcd_docker 3: Incorporate docker based etcd integration package into unittests.

PR 3 for #4144

High level approach is as described in #4144 .

This PR incorporates the new test package into our unittests. Usage is via the `etcdintegration` package, which
makes it transparent to the test code; it simply gets an etcd server started via different means.

One piece of weirdness to call out here: the package currently relies on autosync being *disabled* on the client side.
This is because the advertise client URL (aka what etcd tells clients to connect to) isn't correct for the open port on the host.

That is we have:

- etcd: listen on container port 0.0.0.0:2379, advertise 0.0.0.0:2379
- docker: expose etcd port 2379 to 0.0.0.0:0 on host machine (random free port)
- client: connect to etcd via host machine.

We could probably make this better.

commit-id:263fed13

Author: andrewmains12

src/aggregator/integration/election.go

@@ -51,6 +51,7 @@ func newTestCluster(t *testing.T) *testCluster {
 		t: t,
 		cluster: integration.NewCluster(t, &integration.ClusterConfig{
 			Size: testClusterSize,
+			//	UseBridge: true,
 		}),
 	}
 	return cluster

src/aggregator/integration/multi_server_resend_test.go

@@ -1,5 +1,4 @@
 //go:build integration
-// +build integration
 
 // Copyright (c) 2018 Uber Technologies, Inc.
 //