remote builds failures used to be signaled via exit status 1 of the
build hook, which in turn only happened because the build errors we
got from remote stores was thrown and bubbled up to main which then
logged the error and exited with code 1. with rpc we cannot do this
any more. barring a rewrite of the worker infra to allow for errors
being reported with something other than process exit codes this is
the best can do. ideally we would wrap remote builds in a new goal.
(and then remove all exit code shenanigans from DerivationGoal too)
fixes#928
Change-Id: Idc3ede3cbaca34c8c8e40247da52794f2a5013b9
eldritch horrors
72cad8918b