Use Kolibri hooks for storage hooks.

[rtibbles]

Summary

• Final update for hooking into the Job storage class
• Adds the ability to hook into jobs being cleared
• Also cleans up the way that hooks are registered to use a proper Kolibri hook rather than creating parallel mechanisms

References

In support of learningequality/kolibri-installer-android#119

Reviewer guidance

Create a mock hook derived from the StorageHook and register it somewhere, for example:

@register_hook
class StorageHookExample(StorageHook):
    def schedule(self, job, orm_job):
        print("Job {} scheduled".format(job.job_id))
    
    def update(self, job, orm_job, state=None, **kwargs):
        print("Job {} updated".format(job.job_id))
    
    def clear(self, job, orm_job):
        print("Job {} cleared".format(orm_job.id))

Then run Kolibri and see that the hook properly does these print statements.

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

[github-actions]

Build Artifacts

Asset type	Download link
PEX file	kolibri-0.16.0a11.dev0_git.68.g62c70219.pex
Windows Installer (EXE)	kolibri-0.16.0a11.dev0+git.68.g62c70219-unsigned.exe
Debian Package	kolibri_0.16.0a11.dev0+git.68.g62c70219-0ubuntu1_all.deb
Mac Installer (DMG)	kolibri-0.16.0a11.dev0+git.68.g62c70219-0.3.0.dmg
Source Tarball	kolibri-0.16.0a11.dev0+git.68.g62c70219.tar.gz
WHL file	kolibri-0.16.0a11.dev0+git.68.g62c70219-py2.py3-none-any.whl

[marcellamaki]

Approving following code walk through with @rtibbles