Fix bug 1232: k8scluster-list now shows the vim name it belongs to

VIM name is shown instead of VIM ID.
Similar code was already used in different places, so it has been
properly refactored through the function get_vim_name

Change-Id: I46137f0e17762786036b1cacbbbc043fad0d488f
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>