x/build: all packet builders missing

[dmitshur]

From https://farmer.golang.org/#health:

# "packet" status: Packet linux/arm64 machines
# Notes: https://github.com/golang/build/tree/master/env/linux-arm64/packet
Warn: packet01 missing, not seen for 6h27m13s
Warn: packet02 missing, not seen for 6h3m48s
Warn: packet03 missing, not seen for 6h31m47s
Warn: packet04 missing, not seen for 6h30m30s
Warn: packet05 missing, not seen for 5h41m38s
Warn: packet06 missing, not seen for 6h0m1s
Warn: packet07 missing, not seen for 7h31m44s
Warn: packet08 missing, not seen for 7h34m37s
Warn: packet09 missing, not seen for 6h26m37s
Warn: packet10 missing, not seen for 6h4m54s
Warn: packet11 missing, not seen for 6h9m1s
Warn: packet12 missing, not seen for 7h33m45s
Warn: packet13 missing, not seen for 7h30m4s
Warn: packet14 missing, not seen for 6h31m2s
Warn: packet15 missing, not seen for 6h10m24s
Warn: packet16 missing, not seen for 6h2m2s
Warn: packet17 missing, not seen for 7h31m0s
Warn: packet18 missing, not seen for 6h7m12s
Warn: packet19 missing, not seen for 7h32m28s
Warn: packet20 missing, not seen for 5h44m56s
Error: 20 machines missing, 100% of capacity

This needs investigation and fixing. Previous issue with packet builders was #32543.

/cc @andybons @toothrot

[dmitshur]

SSHing into the machine works okay. I'm going to try rebooting it, a safe operation, as the first step.

[dmitshur]

Restarting the machine fixed the issue (yet again; see details in the linked issue above and previous ones linked from there).