Move Haproxy checks from deployer to release-tools

Proposal

As part of a single coordinator pipeline move Haproxy checks to release-tools

Responsibilities

Ensures that all servers for an environment are READY or in MAINT before we proceed with a deploy

We use Ansible inventory to get the list of HAProxy servers but since that is sourced from the Chef server we could also do it in a ruby script. Example of getting HAProxy in chatops could be modified for this.

Dependencies

• ops.gitlab.net

Notes from &154 (comment 458222928)

This could go either way to me. In release-tools it might make sense to perform this check before we even trigger the deployer pipeline; on the other hand, it makes more sense to me to be in the deployer as its kind of "pre-flight check".