KubernetesClient related refactorings

PR #761

• Simplified KubernetesClient to not read the user id_token from HTTP request (this can't be always done, e.g. if in the context of a background worker)
• Above allowed me to write some tests [1] [2] for this class
• Remove the implicit read of the id_token required me to be sure that all places where a KubernetesClient is instantiated (and their client code) always pass the id_token when performing an operation against the kubernetes API. This is done in this two commits:
  • change to cluster. restart_tool_deployment()
  • change to the rest of cluster functions (functions using cluster. list_tool_deployments() directly or indirectly)
• also fixed use of unimported helm.HelmError in cluster module