[reconfigurator] background task for marking VMMs to be stopped for update - #11170

control: job assigned to worker 01M113V6H4THXEH4Z9AM46J8SC [factory aws, i-0dd5c080b664a7106] (queued for 50 s)
...
task: starting task 0: "setup"
task: process exited: duration 4119 ms, exit code 0
...
task: starting task 1: "rust-toolchain"
task: process exited: duration 15661 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 13924 ms, exit code 0
...
task: starting task 4: "build"
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| info: running `cargo check --bins` on zone-setup (377/377)
| warning: profile package spec `blake2b_simd` in profile `dev` did not match any packages
| warning: profile package spec `rust-argon2` in profile `dev` did not match any packages
|     Checking uzers v0.12.2
|     Checking zone-setup v0.1.0 (/work/oxidecomputer/omicron/zone-setup)
|     Finished `dev` profile [unoptimized + debuginfo] target(s) in 1.72s
| 
| real    14:26.252913720
| user    21:43.494032836
| sys      4:26.159856404
| trap        0.337183437
| tflt        0.639501360
| dflt        0.917683801
| kflt        0.019630195
| lock  1:30:14.587402158
| slp   1:42:55.988885424
| lat        57.712635318
| stop     4:11.775341569
task: process exited: duration 999712 ms, exit code 0
|W| found 0 output files