Add more context to errors returned by config validation (#459)
Add more context to errors returned by config validation (#459)

* Add more context to errors returned by config validation

* shuffle stuff around to meet line limits, fix typos


Former-commit-id: 022b85536f370e340ba318a44d130c687bbd986d
frankbu/istio,sebastienvas/istio,istio/istio,geeknoid/istio,sebastienvas/istio,sebastienvas/istio,frankbu/istio,sebastienvas/istio,frankbu/istio,mandarjog/istio,mandarjog/istio,smawson/istio,istio/istio,frankbu/istio,sebastienvas/istio,istio/istio,frankbu/istio,smawson/istio,frankbu/istio,istio/istio,geeknoid/istio,istio/istio,smawson/istio,mandarjog/istio,geeknoid/istio,smawson/istio,geeknoid/istio,mandarjog/istio,geeknoid/istio,smawson/istio,smawson/istio,geeknoid/istio,mandarjog/istio