set image param as optional for boot from volume

[jichenjc]

What this PR does / why we need it:

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 #763

Special notes for your reviewer:

1. Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

TODOs:

• squashed commits
• if necessary:
  • includes documentation
  • adds unit tests

/hold

[hidekazuna]

/lgtm

[sbueringer]

@jichenjc so basically we're relying on that the user knows what he's doing without validation on our side?

[jichenjc]

@jichenjc so basically we're relying on that the user knows what he's doing without validation on our side?

The validation is done at Openstack or gophercloud layer...
I understand we'd better to add some validation, but seems rely on openstack API validation is more stable and flexible

[sbueringer]

Just wanted to confirm. Fine for me for now. Better than enforcing some false validation like making the image mandatory when in fact it isn't.
/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jichenjc, sbueringer

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[jichenjc]

thanks :)

/hold cancel