[WIP] feat(image): Add initial support for Ubuntu images

[anup-kodlekere]

What this PR does / why we need it:
Enables support for building ubuntu images via pvsadm, exports to .ova format for consumption in IBM Cloud PowerVS.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #799

Special notes for your reviewer:

**Output/Demonstration

I0617 04:07:[35.335351 298077](tel:35335351298077) qcow2ova.go:270] Preparation completed
I0617 04:07:[35.335418 298077](tel:35335418298077) qcow2ova.go:272] Creating an OVA bundle
I0617 04:07:[53.007036 298077](tel:53007036298077) qcow2ova.go:277] OVA bundle creation completed: /tmp/qcow2ova3066092494/ub.ova
I0617 04:07:[53.007116 298077](tel:53007116298077) qcow2ova.go:279] Compressing an OVA file
I0617 04:08:[13.184679 298077](tel:13184679298077) qcow2ova.go:285] OVA file Compression completed


Successfully converted Qcow2 image to OVA format, find at /home/ubuntu/pvsadm/ub.ova.gz
OS root password: <os-root-password>

[ppc64le-cloud-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: anup-kodlekere
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[ppc64le-cloud-bot]

Welcome @anup-kodlekere! It looks like this is your first PR to ppc64le-cloud/pvsadm 🎉

[ppc64le-cloud-bot]

Hi @anup-kodlekere. Thanks for your PR.

I'm waiting for a ppc64le-cloud member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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