iotests: Add test for unsupported image creation

Add a test for creating and amending images (amendment uses the creation
options) with formats not supporting creation over protocols not
supporting creation.

Cc: qemu-stable@nongnu.org
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>