Updating util/nrl/batch_install.sh: CARGO env vars etc

[climbfuji]

Description

This PR updates util/nrl/batch_install.sh:

• Add CARGO environment variables before fetch_cargo_deps.py; with this change, fetching the rust/cargo dependencies works on some of the NavyDSRC login nodes, but not on all.
• Reduce number of concurrent packages being built
• Use walltime 720 minutes unconditionally when submitting build to queue

Dependencies

None

Issues addressed

None

Applications affected

None

Systems affected

NRL systems

Testing

• CI: Note whether the automatic tests (GitHub actions tests that run automatically for every commit) pass or not
  • GitHub actions CI tests pass
  • GitHub actions CI tests do not pass (provide explanation)
  • GitHub actions CI tests skipped (provide explanation if necessary)
• New tests added: List and describe any new tests added to GitHub actions
  • ...
• Additional testing: Add information on any additional tests conducted
  • ...

Checklist

• This PR addresses one issue/problem/enhancement or has a very good reason for not doing so.
• These changes have been tested on the affected systems and applications.
• All dependency PRs/issues have been resolved and this PR can be merged.
• All necessary updates to the documentation (spack-stack wiki) will be made when this PR is merged