[Create] store helm certificates in Kubernetes secrets

[petermikitsh]

Currently, snow create will write to the user's ~/.helm directory, creating a bunch of files:

• ca.cert.pem
• ca.key.pem
• helm.cert.pem
• helm.csr.pem
• helm.key.pem
• tiller.cert.pem
• tiller.csr.pem
• tiller.key.pem

This is problematic if we want to use snow with different clusters-- running snow create repetitively would overwrite the old files. Additionally, if you run snow create in a CI environment, it's possible you might lose the files forever.

To keep things portable, these files should be stored as Kubernetes secrets, and retrieved as necessary.

[petermikitsh]

Upgrading to Helm 3 will solve this problem. The tiller client is eliminated, so no need to generate certificates.