Helm chart should read image registry name from global.imageRegistry variable

[rbcek]

Describe the problem/challenge you have
To use my-image-registry as image registry I have to specify for each setup:

localpv:
  image:
    registry: "my-image-registry/"
helperPod:
  image:
    registry: "my-image-registry/"

Describe the solution you'd like
Usage of global.imageRegistry, which is commonly used would be perfect (without need to append '/' at the end):

global:
  imageRegistry: "my-image-registry"

Anything else you would like to add:
Probably this value should be used as default. Values provided as localpv.image.registry or helperPod.image.registry should overwrite default value.

[niladrih]

Yep, I see how this could be useful.