[manila-csi-plugin] make auth more tolerant

[mandre]

What this PR does / why we need it: Remove dependency on a couple of fields where the logic was wrong. For example, these fields do not necessarily depend on a password being set, as we could be using application credentials.

This prevents manila driver from entering an error state when it finds unnecessary fields in the clouds.yaml. It now simply ignores them.

Which issue this PR fixes(if applicable):

Fixes #2757

Special notes for reviewers:
The fix is in pkg/client/client.go so presumably affects all binaries?

Release note:

Make authentication more tolerant to unneeded fields

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[kayrus]

I never had issues with application credentials and manila CSI. Are you sure this is not related to a cloud.yaml parser code?

[mandre]

@kayrus I have provided more context in the related issue. You'll get an error when using application credentials, and leaving username in the auth options. One could argue that the clouds.yaml is invalid and should then be rejected, but openstack SDK and other components in kubernetes happily takes it and ignores the extra options. The fact that the manila driver errors on clouds.yaml is a surprising behavior IMO. I propose to loosen some validations and make the auth parsing more tolerant.