OpenStack driver: Add support for scheduler hints on compute server creation

[rodcloutier]

The OpenStack api for compute allows to specify data for the scheduler in the form of an additional fields in the /server POST api route. See the OpenStack api-ref Create Server for more detailed informations.

docker-machine should provide the appropriate flags to configure the hints.

We are willing to work on this and submit segmented PRs for the changes.

[dr4Ke]

Looking at the code, I guess that we would need to use the gophercloud/gophercloud package since rackspace/gophercloud compute extensions don't include schedulerhints. See https://pkg.go.dev/github.com/rackspace/[email protected]/openstack/compute/v2/extensions?tab=subdirectories