Spack module tweeks to make compatible across supported images

[nick-stroud]

The Spack modules were tested across the following operating systems:

      instance_image:
        family: hpc-centos-7
        project: cloud-hpc-image-public

      instance_image:
        family: hpc-rocky-linux-8
        project: cloud-hpc-image-public

      instance_image:
        family: debian-11
        project: debian-cloud

      instance_image:
        family: ubuntu-2004-lts
        project: ubuntu-os-cloud

Fixes in this change:

• source is not available in default shell for Ubuntu and Debian
• Explicitly call bash for command execution to maintain bash pipefail option
• python package is not defined for rocky.

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• Add or modify unit tests to cover code changes
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