Workflow for upgrading Salt

[aneeshusa]

Homebrew has packaged Salt 2015.8.1 so I'll put in a PR to update the pinned salt version soon. However, upgrading Salt requires some extra care for two reasons:

1. It's best to restart the service when the package is updated to keep the installed and running versions in sync, but restarting a master or minion service will interrupt an ongoing highstate.
2. Masters need to be updated before minions, but salt '*' state.highstate cannot enforce ordering - Salt's orchestration can help with this.

I want to make sure there is a concrete plan for this and future Salt version upgrades to prevent breakage. Do you currently have a workflow for updating Salt? If not, I think manual updates are fine for now since there are so few machines: first on the salt master, then on the minions. I'll look into adding some automation to this.

[aneeshusa]

Blocked on saltstack/salt#29098.

[edunham]

@aneeshusa for the "document the workflow" part of this issue, I've moved the Salt docs into their own wiki page at https://github.com/servo/servo/wiki/SaltStack-Administration.

It looks like the Salt issue that this was previously blocked on is now resolved.

[aneeshusa]

Great, closing since we've agreed on manual updates for now.