Changes

jobs/{master,gerrit}: set ulimit filesize to 1 GiB

Set a max file size limit of 1 GiB via ulimit. This prevents jobs from
filling up the disk by generating one huge log file.

I have chosen 1 GiB as limit, because jobs that clone linux kernel
repos may have packed git artifacts that are several 100 MiB in size.

It would be even better to set the overall max disk space that can be
used from one "docker run" call, but this is currently not supported for
ext4: https://github.com/moby/moby/issues/29364

Related: OS#6704
Change-Id: I4f9d5ad33c2d6e003d239e8b2c97753d64dd00f6