linux1b bot isn't working

[Aatch]

The linux1b bot is the only bot servicing snapshots and it just can't do it. It takes hours to even fail, which suggests that isn't hanging, but instead is thrashing and occassionally coughs up a few bytes which keeps the buildbot master happy.

I cancelled it building a snapshot after 10 hours, and the most recent failure was it killed after 6.

@graydon @brson this is blocking a new snapshot

[huonw]

Triage visit: appears to be working fine now (the most recent build took 2.5hrs and was successful).