bug#24496: offloading should fall back to local build after n tries

[ng0]

When I forgot that my build machine is offline and I did not pass
--no-build-hook, the offloading keeps trying forever until I had to
cancel the build, boot the build-machine and started the build again.

A solution could be a config option or default behavior which after
failing to offload for n times gives up and uses the local builder.

Is this desired at all? Setups like hydra could get problems, but for
small setups with the same architecture there could be a solution beyond
--no-build-hook?
-- 
              ng0