Add trooper documentation for CT bots and for iOS "the service is invalid"

site/dev/sheriffing/trooper.md

 Infra Trooper Documentation
 ===========================
 
 ### Contents ###
 
 *   [What does an Infra trooper do?](#what_is_a_trooper)
 *   [View current and upcoming troopers](#view_current_upcoming_troopers)
 *   [How to swap trooper shifts](#how_to_swap)
 *   [Tips for troopers](#tips)
 
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   - Disconnected devices (these are detected as the "wait for device" step failing)
 
 - "Failed to execute query" may show a different query than the failing one;
   dismiss the alert to get a new alert showing the query that is actually
   failing. (All "failed to execute query" alerts are lumped into a single alert,
   which is why the failed query which initially triggered the alert may not be
   failing any more but the alert is still active because another query is
   failing.)
 
 - Where machines are located:
-  - Machine name like "skia-vm-NNN" -> GCE
+  - Machine name like "skia-vm-NNN", "ct-vm-NNN" -> GCE
   - Machine name ends with "a3", "a4", "m3" -> Chrome Golo
+  - Machine name ends with "m5" -> CT bare-metal bots in Chrome Golo
   - Machine name starts with "skiabot-" -> Chapel Hill lab
   - Machine name starts with "win8" -> Chapel Hill lab (Windows machine
     names can't be very long, so the "skiabot-shuttle-" prefix is dropped.)
   - slave11-c3 is a Chrome infra GCE machine (not to be confused with the Skia
     Buildbots GCE, which we refer to as simply "GCE")
 
 - The [chrome-infra IRC channel](https://comlink.googleplex.com/chrome-infra) is
   useful for questions regarding bots managed by the Chrome Infra team and to
   get visibility into upstream failures that cause problems for us.
 
@@ skipping 12 matching lines @@
 
 - If there is a problem with a bot in the Chrome Golo or Chrome infra GCE, the
   best course of action is to
   [file a bug](https://code.google.com/p/chromium/issues/entry?template=Build%20Infrastructure)
   with the Chrome infra team. But if you know what you're doing:
   - To access bots in the Chrome Golo,
     [follow these instructions](https://chrome-internal.googlesource.com/infra/infra_internal/+/master/doc/ssh.md).
     - Machine name ends with "a3" or "a4" -> ssh command looks like `ssh
       build3-a3.chrome`
     - Machine name ends with "m3" -> ssh command looks like `ssh build5-m3.golo`
+    - Machine name ends with "m5" -> ssh command looks like `ssh build1-m5.golo`.
+      [Example bug](https://bugs.chromium.org/p/chromium/issues/detail?id=638193) to file to Infra Labs.
     - For MacOS and Windows bots, you will be prompted for a password, which is
       stored on [Valentine](https://valentine.corp.google.com/) as "Chrome Golo,
       Perf, GPU bots - chrome-bot".
   - To access bots in the Chrome infra GCE -> command looks like `gcutil
     --project=google.com:chromecompute ssh --ssh_user=default slave11-c3` (or
     use the ccompute ssh script from the infra_internal repo).
 
 - Read over the [SkiaLab documentation](../testing/skialab) for more detail on
   dealing with device alerts.
 
 - To stop a buildslave for a device, log in to the host for that device, `cd
   ~/buildbot/<slave name>/build/slave; make stop`. To start it again,
   `TESTING_SLAVENAME=<slave name> make start`.
 
 - Buildslaves can be slow to come up after reboot, but if the buildslave remains
   disconnected, you may need to start it manually. On Mac and Linux, check using
   `ps aux | grep python` that neither buildbot nor gclient are running, then run
   `~/skiabot-slave-start-on-boot.sh`.
+
+- Sometimes iOS builds fail with 'The service is invalid'. Try rebooting the iOS host to fix this.