ui: Fix check about setting ssh keys to machine

Fix the check about setting ssh keys to a new machine. Besides the
operating system of the image we must also check if the properties of
the image specify that the 'EnforcePersonality' task or all tasks will
be excluded. Also, if the image has no properties, than it is equivalent
with exclude all tasks.
ui: Check whether image supports to change pass

Extend 'supports' of the image model to properly check whether an image
supports to set a password or not.
ui: Hide password if image do not support pass

Make the final step of the VM creation wizard to not display the
password of the VM, if it using an image that does not support
setting a password (e.g. snapshots).