Fix bugs and improve monitoring support

Fixed test setup issue and missing cleanup of monitoring firewall rules.
Added logic to generate an unique password for Grafana as part of Cluster bring up
Modified the pod description to always use the 'latest' image to avoid pulling all the tags, thereby reduce startup latency.

Replaces #2240 

cc @filbranden 
This will not work under `set -o errexit`. Instead, put the command inside an "if" condition:

```shell
  if "${kubectl}" create -f ... && "${kubectl}" create -f ... && "${kubectl}" create -f ...; then
    echo "Failed to set up monitoring"
    teardown-monitoring
  else
    dashboardIP=...
```