ui: Add check about which images support password

Add check about which images support setting a new password new
machines. Namely, check if the image has the 'EXCLUDE_ALL_TASKS' or
'EXCLUDE_TASK_CHANGEPASSWORD' image properties.
ui: Hide password when image does not support it

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).