[reconfigurator] background task for stopping marked VMMs - #11380

control: job assigned to worker 01M5XVP1BTJSZM87X56DM583C8 [factory aws, i-0939507f5ca73ae5f] (queued for 49 s)
...
task: starting task 0: "setup"
task: process exited: duration 4125 ms, exit code 0
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task: starting task 1: "rust-toolchain"
task: process exited: duration 17156 ms, exit code 0
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task: starting task 2: "authentication"
task: process exited: duration 16 ms, exit code 0
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task: starting task 3: "clone repository"
task: process exited: duration 12586 ms, exit code 0
...
task: starting task 4: "build"
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|  Documenting omicron-uuid-kinds v0.1.0 (/work/oxidecomputer/omicron/uuid-kinds)
|  Documenting dev-tools-common v0.1.0 (/work/oxidecomputer/omicron/dev-tools/common)
|     Finished `dev` profile [unoptimized + debuginfo] target(s) in 7m 18s
| warning: the following packages contain code that will be rejected by a future version of  [...]
| note: to see what the problems were, use the option `--future-incompat-report`, or run `ca [...]
|    Generated /work/oxidecomputer/omicron/target/doc/api_identity/index.html and 206 other  [...]
| 
| real     7:18.735836983
| user    14:03.163751856
| sys      3:37.328248027
| trap        0.178526240
| tflt        0.003543537
| dflt        0.032479309
| kflt        0.000042362
| lock  6:44:01.470085069
| slp   2:34:26.977089521
| lat        21.933942781
| stop     1:50.480525214
task: process exited: duration 802382 ms, exit code 0
|W| found 0 output files