bug#18553: Hydra: failures to create GC root /home/hydra/offload-*

[Mark H Weaver]

I've seen several failed builds on Hydra where the build log ends with
something like this:

--8<---------------cut here---------------start------------->8---
phase `strip' succeeded after 0 seconds
@ build-succeeded 
/gnu/store/b20viwrr0h5y2mqdpx9bpi21snb4fv5c-xkeyboard-config-2.6.drv -
/gnu/store/sp60mrd8hashvh0v8l17gn2mz87a34kl-xkeyboard-config-2.6
guix build: error: failed to create GC root 
`/home/hydra/offload-20121227-hydra.gnu.org-18304': File exists
--8<---------------cut here---------------end--------------->8---

Simply restarting the jobs typically result in successful builds.

     Mark