Add support for images import/export in CDK/minishift adapter

Would be fine if we could manage images export/import for the CDK/Minishift server adapter. This is how it could be implemented:

• in the UI we could display the list of available images (using the Docker connection)
• in the UI we could also display the list of cached images (from the minishift images list command)

Then using context menu we could import/export images when one of them is selected