Update metrics base image to proton 0.18
Update metrics base image to proton 0.18

This fixes #457

EnMasseProject/enmasse,EnMasseProject/enmasse,jenmalloy/enmasse,jenmalloy/enmasse,EnMasseProject/enmasse,jenmalloy/enmasse,EnMasseProject/enmasse,EnMasseProject/enmasse,EnMasseProject/enmasse,jenmalloy/enmasse,jenmalloy/enmasse,EnMasseProject/enmasse,jenmalloy/enmasse,jenmalloy/enmasse