Fix a segfault when collecting the storage size metrics when the getters
used to collect the data on etcd haven't been initialized properly. This
happens when the EtcdOptions are not applied which is the case for
aggregated apiservers that don't care about storage.
Signed-off-by: Damien Grisonnet <dgrisonn@redhat.com>
Kubernetes-commit: c6efaf16c1ed07ce37485b7a272628f653cbf06f