Undeploy: Export DEPLOYMENT_TARGET before removing environments

[CodeGat]

Closes #242

Background

A curious regression introduced in #218, is that now that we can (and have, in ACCESS-TEST Prereleases) use the set-at-install-time environment variable DEPLOYMENT_TARGET in our spack.yamls, spack expects it to be set. Interestingly, spack now errors out when it can't find it, since it loads config from all existing environments spack.yaml while uninstalling some environments, including ones that require DEPLOYMENT_TARGET.

The PR

In this PR:

• export DEPLOYMENT_TARGET before undeploying environments

Testing

Tested uninstallation of a dummy enviroment in Prerelease without exporting DEPLOYMENT_TARGET which fails as expected.
Exported DEPLOYMENT_TARGET and then attempted uninstallation, which succeeded.

[harshula]

🤞

[atteggiani]

Looks good!

Just a general comment on DEPLOYMENT_TARGET and the spack.yaml file.
I am not sure of all the possible values of DEPLOYMENT_TARGET but I believe it would be something like Gadi, Setonix, etc.
Isn't there a way to have spack automatically detect the DEPLOYMENT_TARGET (from the hostname of the machine where it is run for example), if no explicit DEPLOYMENT_TARGET is set within the environment?

[CodeGat]

That is true @atteggiani, and indeed users can specify that in their spack.yaml via when: re.match("gadi.nci.org.au", hostname), but there may be a time where we have multiple spack instances outside of the Gadi [Pre]Release ones on Gadi. For example, maybe a Test spack instance or something, that has different requirements than Prerelease.

[CodeGat]

See succeeding run: https://github.com/ACCESS-NRI/ACCESS-OM2/actions/runs/13710579242/job/38348497257