Multiple helm repo updates

[poblin-orange]

For a given helm kubectl bosh deployment, declaring multiple helm repositories, each repo gives a helm repo update, resulting in very slow errand execution.
More over, when using helm kubectl repo mirroring, all the declared repos target the same virtual repo (micro-depls hosted jcr), so this updates are useless.

Changing the helm repo implementation witn n helm repo add command, and a single helm repo update would give a huge perf boost to the errands