Pass extraVolumes last for -config-dir

[lkysow]

This will allow user-defined config to override any config set in the
helm-created config map because Consul will override previous
configuration with the last -config-dir.

For example, this user (hashicorp/consul-k8s#220) wants to specify the "acl": {"down_policy": "your-policy"} config which is set in /consul/aclconfig by the helm chart (technically it's written by consul-k8s acl-init). By swapping the ordering here, they can now create their own configmap which sets

"acl": {"down_policy": "their-policy"}

and pass it in via

client:
  extraVolumes:
  - type: configMap
     name: my-config-map
     load: true

And that single key will be overridden.

Fixes hashicorp/consul-k8s#220

[kschoche]

Looks great!

[thisisnotashwin]

NICE!