Fetching correct image straight from images API

Currently, rsCloudServersOpenstack fetches a list of all images from the images API and then filters the one that matches with the name passed into it. This caused issues in the LON datacenter as apparently the API is paginating at 25 items per page by default (the US endpoints apparently don't do that) and the first page actually only contained Linux images. I think the best fix for that is to use the name=<name> URI parameter so that only the one matching image is returned. I have tested this and it works.

Please merge or let me know if this requires fixing of any kind.

Thanks,
Nico