[WIP] Connection Healthcheck option

[sideangleside]

Based upon a few requests I have gotten, I want to propose the following patch to check the health of a Foreman installation prior to registration. The general premise being:

• connect to https://FOREMAN:API_PORT/katello/api/ping
• Check the services to ensure that
  • all of them report OK as their status
  • they are not too busy (defined by a user-configurable value)

If the services fail the health-check, exit, and remove the katello-ca-consumer-latest package.

Questions that I have:

• is a response time of 1000 milliseconds an appropriate amount of time to consider a service too busy to service clients
• should we finish up #209 in this PR? (In that PR, we were attempting to validate creds before installing the katello-ca-consumer-latest RPM, which I don't think we need to do. (assuming we clean up if the creds fail).

[evgeni]

I think 1000ms is enough, but I've long not seen heavy used katello installs :woman_shrugging:

One thing that bothers me with this setup: we do changes to the bootstraped system, before telling "oh, no, we won't bootstrap today". And while we do try to revert those changes (you clean the ca rpm), the system is not (might not) be bit-identical as before. So yes, I think piggy-backing this ontop of #209 and making it not even install the CA RPM would be awesome.

(My worry case is when migrating from one Katello to another, we already removed the old CA rpm, but we cannot reliably restore it and thus leave the machine without updates)