Fix cassandra test about updated_on ttl
Fix cassandra test about updated_on ttl

We can't use freezegun here since creating/updating metric
now() is computed inside cassandra queries (outside python).

Signed-off-by: Thibault Chataigner <760b602e41777d70d0be9acf5dc7a32f8153d50b@criteo.com>

criteo/biggraphite,iksaif/biggraphite,iksaif/biggraphite,Thib17/biggraphite,Thib17/biggraphite,iksaif/biggraphite,criteo/biggraphite,Thib17/biggraphite,iksaif/biggraphite,criteo/biggraphite,Thib17/biggraphite,criteo/biggraphite