Interfaces should only validate values they're going to use. Boot
interfaces do not care about image properties when local boot is used
(which is the default), so they shouldn't validate them. The deploy
interface has to provide validation for images.
This change fixes PXE, iPXE and redfish-virtual-media, although other
boot interfaces may need a similar change. We also need to refactor
handling instance_info in deploy_utils, but that can wait until the
iSCSI deploy removal.
Also refactor unit tests for redfish-virtual-media.
Story: #2008874
Task: #42418
Change-Id: Ida21f21d6435c0d7fa46cb5b1161f034ad8956ee
(cherry picked from commit e6bb99cd8f)
0500fe1072