etcd_docker 4: Incorporate docker based etcd into Go integration tests (#4148)

[andrewmains12]

PR 4 for #4144

High level approach is as described in #4144 .

This PR integrates docker based etcd into our Go integration tests. It removes the need to have the embed package running
in m3db for them, but doesn't yet touch that functionality.

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Stack:

• etcd_docker 3: Incorporate docker based etcd integration package into… (#4147) #4155
• etcd_docker 2: Add a docker based etcdintegration package #4154
• etcd_docker 1: Refactor resources/docker package into resources/dockerexternal, resources/dockerm3, x/dockertest (#4145) #4153

⚠️ Part of a stack created by spr. Do not merge manually using the UI - doing so may have unexpected results.