pinNamespaces: set capacity for returnedNamespaces
pinNamespaces: set capacity for returnedNamespaces

We know the size of the slice already, so let's set its capacity in
advance.

Signed-off-by: Kir Kolyshkin <3a017b8ddb3f9cf3e4a59978b004111bdeb97f08@gmail.com>

kubernetes-incubator/ocid,kubernetes-incubator/ocid,kubernetes-incubator/ocid,nalind/cri-o,kubernetes-incubator/cri-o,nalind/cri-o,kubernetes-incubator/cri-o,kubernetes-incubator/cri-o,kubernetes-incubator/cri-o,nalind/cri-o