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 #2293 and #2240

cc @vishh and @brendanburns 
'latest' tag is not needed.