Prune in-memory blocks from missing tenants

[dgzlopes]

What this PR does:
If a tenant disappears blocks are pruned from the in-memory blocklist.

Which issue(s) this PR fixes:
Fixes #285

Checklist

• Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[annanay25]

Thanks for working on this @dgzlopes! I've left some comments.

[joe-elliott]

To add to Annanay's comments, I would like a test that covers this. Please just ask if you'd like some guidance on building a test, I know they're a little intense at the moment.

[dgzlopes]

Moved the code into a len(blockIDs) == 0 block and changed the log level to info.

Okey @joe-elliott!

I'm diving into the tests, and well, they look fun. I'll try to add the coverage for this PR. If I'm blocked I'll ask for some guidance 😄

[dgzlopes]

Added a test. I'm not sure if it's OK... it's my first test in Go 😄

I re-used TestRetention code, but this time before calling pollBlocklist() I remove the testTenantID trace folder. Then, I check if the in-memory blocklists still have the blocks.

[joe-elliott]

Nice work on the tests. Had a couple of suggestions for improvements and it looks like the linter is mad at you.

[joe-elliott]

Basically just looking for some tests directly targeting the cleanMissingTenants method. Leave the existing test and add a TestCleanMissingTenants() test that directly exercises this method.

After that should be ready to go!

[dgzlopes]

Thanks a lot for the patience and the exhaustive review @joe-elliott :)

Fixed the nit and added the test for cleanMissingTenants

[joe-elliott]

nice work @dgzlopes

Thanks!

I believe I need to dismiss this to merge? It says merging is blocked due to changes requested, but it seems like all changes are resolved?