Move to using faas-cli to download kubeseal secret

[Waterdrips]

We should move to using faas-cli to fetch the kubeseal secret from the cluster once its created rather than using bash,
This is now possible because of this feature openfaas/faas-cli#730

Current Behaviour

Bash script is used to pull the secret to the local computer

Possible Solution

Use faas-cli

faas-cli cloud seal --download

This would reduce the operational burden of maintaining the bash scripts