[Engineering] Change to SWAT deploy (aka "let's not break things")

[Greg Grossmeier]

Hello!

For a while we've had the ability to test changes in production on a
single host (mw1017) using a special HTTP header (X-Wikimedia-Debug).
This has proved useful for many when deploying changes in production and
we are adding it to the SWAT deploy process.

See the steps at:
https://wikitech.wikimedia.org/wiki/SWAT_deploys#Doing_the_deploy

Namely:
4. After merge, the SWAT team member fetches the patch(es) to tin and then
   runs scap pull on mw1017
5. The submitter tests the change by using the instructions at
   X-Wikimedia-Debug#Staging_changes AND the SWAT team member checks the
   error logs
6. If there are no errors and the fix seems to work (if testable in that
   manner), then then SWAT team member deploys the patch to the entire
   fleet

How to test on mw1017:
https://wikitech.wikimedia.org/wiki/X-Wikimedia-Debug#Staging_changes

To less exciting SWAT deploys,

Greg

-- 
| Greg Grossmeier            GPG: B2FA 27B1 F7EB D327 6B8E |
| identi.ca: @greg                A18D 1138 8E47 FAC8 1C7D |
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