loggr-system-metric-scraper debug port should be configurable

[ameowlia]

What

As a CF operator
I want to know which ports system components are using on the TCP Router VM
So that I can make sure they don't overlap with tcp router ports
So that my tcp router doesn't silently break. See issue here.

Steps to reproduce

1. Deploy with the loggr-system-metric-scraper on any VM
2. ssh onto that VM
3. run netstat -tlpn | grep system-metrics
4. note the ports it is running on
5. run monit restart loggr-system-metric-scraper
6. run netstat -tlpn | grep system-metrics
7. see that one of the ports here does not match the ports from step 4

Expected

I want to be able to set the debug port as a bosh property and to have it respected.

Actual

The debug port is any random open port.

Technical Details

See the technical details for this 99% identical bug: cloudfoundry/loggregator-agent-release#44

I will submit a PR for this soon.

[cf-gitbot]

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[ameowlia]

Per this doc, we should try to have the default port be 14921. If that is impossible, please update said doc.

[ameowlia]

Oops, 14921 is the metrics.port for the leader-election-agent job. This job isn't on the TCP Router, but they are both on other VMs.

[ameowlia]

Closing because it turns out I wanted system-metrics-agent job from the system-metrics release 🤦‍♀️