openstackclient: Add python-barbicanclient dep

[baurmatt]

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[github-actions[bot]]

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[baurmatt]

Hey @chenrui333, as you've reviewed a few PRs of openstackclient in the past, do you mind taking a look at this one as well? :)

barbican is e.g. required for Octavia loadbalancers with terminated HTTPS.

[branchv]

Thanks for the PR and sorry this got overlooked! #176382 was just merged with the same change