We only have 8GB on the Brya Chromebook used for venus testing, and the
job is unstable because using all the available RAM causes OOM kills.
So reduce launch_cvd memory limit to 4GB by default, still allowing to
change the default by setting the CUTTLEFISH_MEMORY variable in jobs
that might want a different value.
This change has been inspired by CROSVM_MEMORY, but a new variable is
used because technically cuttlefish can also use qemu in some setups,
not only crosvm.
Signed-off-by: Guilherme Gallo <guilherme.gallo@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35126>
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