runtimevar/etcd: import go.etcd.io/etcd instead of github.com/coreos/etcd

[vangent]

github.com/coreos/etcd has renamed to use package name go.etcd.io/etcd. They are two different packages, and hence some of the packages stops working with go get. could you change to import go.etcd.io/etcd? Thanks.

[vangent]

(filing for @h8liu based on a comment on a pr)

[vangent]

Per @h8liu

Here is an example of build failure trying to build the etcd repo with github.com/coreos/etcd import path:

https://gopkgs.io/builds/20180911-195307-3d66b81f

[h8liu]

the current downside is that etcd has not officially released a version after they changed the import path.. so to support go get, one has to use one that is not compatible with their latest release.

[h8liu]

importing as go.etcd.io/etcd still builds, but will drag in github.com/coreos/etcd because the source is pre-import-path-change.

[vangent]

Yea, I did try to use go.etcd.io/etcd at first, but it keeps pulling in the old coreos/etcd as well, and then I get compatibility errors:

unknown field 'NoFreelistSync' in struct literal of type bolt.Options

master...vangent:etcd-rename shows the go.mod changes that result.

I think we'd prefer to wait until there's an official etcd release with the new name, then we can switch to use it.

[vangent]

Blocked on a version after 3.3.9:
https://github.com/etcd-io/etcd/releases

[vangent]

I tried again with 3.3.10, but got the same problems with coreos things getting pulled in.