[mgmt] Should we move to golang 1.9 and etcd 3.3 ?

[James]

With the release of etcd 3.3 last week, it now requires golang 1.9.
I'm thinking of bumping to this version of etcd, and as a result
moving the minimum golang requirement to 1.9. Does anyone have any
strong objections? If so, please speak up now :) Happy to delay a week
or so if someone needs time to upgrade their dev environment.

At lease one pending patch depends on 3.3, and it's a logical place
we'll need to move to eventually.
https://github.com/purpleidea/mgmt/pull/200

Thanks,
James