cephadm: require --image is passed to inspect-image

cephadm: require --image is passed to inspect-image

The selection of an image by default was likely unused and
has always been a bit of a flaky thing, especially if multiple
clusters are making use of the host where this is run. It seems
preferable to just require this argument. Additionally, the
command without the image specified is currently untested
and prone to being broken. All uses of inspect-image done
through the cephadm mgr module specify the image.

Signed-off-by: Adam King <adking@redhat.com>