ACCESS-OM3 esmf OOM Parallelism Fix

[CodeGat]

The deployment of ACCESS-OM3 is failing because it is being killed by Gadis OOMKiller when installing esmf. This PR explicitly turns down the parallelism to --jobs 4 to reduce the memory used.

See the failures here: ACCESS-NRI/ACCESS-OM3#5

Closes ACCESS-NRI/ACCESS-OM3#8

[CodeGat]

Alternatively, we could have a vars.SPACK_INSTALL_PARALLEL_JOBS var that can be set to --jobs 4 (or not set at all) leading to at least a difference in parallel jobs on a per-model basis. I think that might be better (although it would lead to another thing in the vars context

[CodeGat]

For those with access, I've set vars.SPACK_INSTALL_PARALLEL_JOBS in ACCESS-OM3 https://github.com/ACCESS-NRI/ACCESS-OM3/settings/environments/2707603294/edit to --jobs 4. It is unset in ACCESS-OM2, and shouldn't affect the spack install command, since an unset vars expands to ''

[aidanheerdegen]

Appreciate the additional inline comments. They do assist in scaffolding understanding and comprehension.