Fix sd/etcd and sd/etcdv3 integration test flakes

[peterbourgon]

The sd/etcd and sd/etcdv3 integration tests are extremely flaky. I can generally expect them to trigger build failures on every PR. Here is one example.

I am going to disable those tests until they can be fixed. This issue is a plea for help from the community to fix them.

[26tanishabanik]

@peterbourgon , can you explain the issue? and how it can be reproduced, the example link is invalid