Update images selection pattern

New pattern is: [repository/][image][:version] (image is now optional).
Allow to select images in repository without globbing: 'is list repository/'
now work as 'is list repository/*'.
Same for version, for example: 'is list :*dev' work as 'is list */*:*dev'.

Seblu: Fix few explicit comparaison

Signed-off-by: Sébastien Luttringer <sebastien.luttringer@smartjog.com>