func (sv SupportedVersions) NextVersionPair(current *EtcdVersionPair) *EtcdVersionPair {
	nextVersion := sv.NextVersion(current.version)
	if nextVersion == nil {
		return nil
	}
	storageVersion := storageEtcd3
	if nextVersion.Major == 2 {
		storageVersion = storageEtcd2
	}
	return &EtcdVersionPair{version: nextVersion, storageVersion: storageVersion}
}

// ParseSupportedVersions parses a list of etcd versions.