Remove cherrypy dependency

[rtibbles]

Summary

• Removes cherrypy as a dependency
• Replaces it with explicit use of cheroot and magicbus
• Cleans up unused dependencies
• Passes port to zeroconf listener registration once main server has completed serving
• Has fallback for services command where it will pass in the set port once the process has started running
• Consolidates all server start code in server.py
• Uses pid file to track server status using ProcessBus life cycle hooks
• Use pid file throughout start cycle rather than separate startup lock
• Simplifies the stop procedure
• Sets default zip port to 0 to allow it to be dynamically chosen
• Creates a port cache to record previously available ports - port discovery slows startup time, so this helps to mitigate this
• Directly connect server logging to kolibri logging

References

Depends on #8023
Fixes #8024
Supersedes #7714
This also contributes to fixing learningequality/kolibri-app#74 in a most general way, by allowing apps to just specify port 0, and allowing a free port to be chosen for use.

Reviewer guidance

Kolibri should run and serve as intended.
Appropriate logging happens for all events in the server life cycle.
Start Kolibri with --port=0 and verify that the port bound is the one reported, and that zeroconf registers that port

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Testing checklist

• Contributor has fully tested the PR manually
• If there are any front-end changes, before/after screenshots are included
• Critical user journeys are covered by Gherkin stories
• Critical and brittle code paths are covered by unit tests

PR process

• PR has the correct target branch and milestone
• PR has 'needs review' or 'work-in-progress' label
• If PR is ready for review, a reviewer has been added. (Don't use 'Assignees')
• If this is an important user-facing change, PR or related issue has a 'changelog' label
• If this includes an internal dependency change, a link to the diff is provided

Reviewer checklist

• Automated test coverage is satisfactory
• PR is fully functional
• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

[jredrejo]

Discovering of the zip port is not working fine, as it's not being assigned. Hashi does not work with this PR (and it did work in #8023)

Tested with PLIX, ASP, H5P... none of the html5 apps works as the browser is not using the right port to get the files:

it tries port 8080 while Zip port is 45739:

INFO     Starting on 0.0.0.0:45739
INFO     Waiting for 0.0.0.0:45739
INFO     Serving on 0.0.0.0:45739
INFO     Starting on 0.0.0.0:8080
INFO     Waiting for 0.0.0.0:8080
INFO     Serving on 0.0.0.0:8080
INFO     Registering ourselves to zeroconf network with id '9ad9ee5e19f80c03774f7d3d29dffdc3' and port '8080'
INFO     Kolibri running on: http://172.18.0.1:8080/
INFO     Kolibri running on: http://172.17.0.1:8080/
INFO     Kolibri running on: http://127.0.0.1:8080/
INFO     Kolibri running on: http://192.168.0.44:8080/
INFO     Bus state: RUN

[jredrejo]

Running it forcing the zip port it works:
KOLIBRI_ZIP_CONTENT_PORT=8081 kolibri start --foreground

[jredrejo]

I DO want to delete this review comment but GH does not let me doing it unless I write something :(

[jredrejo]

Now everything works fine, LGTM