iotests: Make verify_virtio_scsi_pci_or_ccw() public

iotests: Make verify_virtio_scsi_pci_or_ccw() public

It has no internal callers, so its only use is being called from
individual test cases. If the name starts with an underscore, it is
considered private and linters warn against calling it. 256 only gets
away with it currently because it's on the exception list for linters.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20230525124713.401149-12-kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>