Support multiple Open edX devstacks

[arbrandes]

Description

This allows for multiple edX devstacks (introduced via https://github.com/edx/devstack/pull/532) by letting the user specify which compose project to target.

It also adds a couple of convenience Makefile targets.

Test Instructions

For the simplest test, pulling in this PR should not affect the maintenance of an existing devstack, or creating a new one as usual.

To actually test the feature introduced here, one must first create a new Open edX devstack using a separate compose project. See the instructions in the README. Then, export OPENEDX_PROJECT_NAME accordingly and check if blockstore provisions and runs correctly.

[openedx-webhooks]

Thanks for the pull request, @arbrandes! I've created OSPR-5021 to keep track of it in JIRA, where we prioritize reviews. Please note that it may take us up to several weeks or months to complete a review and merge your PR.

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[arbrandes]

@bradenmacdonald, as a user of multiple simultaneous devstacks (and blockstores), I've been maintaining this for my own use for a while, but after the latest rebase onto the Python 3.5/3.8 stuff, I'd much rather get this upstream and save me the trouble. (I know blockstore is moving into edx-platform some time soon, but this should still be useful in the meantime.) Mind taking a quick look as Core Commiter?

[bradenmacdonald]

@arbrandes Yes I can, but not until sometime next sprint. Can you get someone else to do a first review in the meantime? If I'm reviewing+merging as Core Committer it should have another review first.

[arbrandes]

@bradenmacdonald, sure thing, and thanks!

[natabene]

@arbrandes Thank you for your contribution.
@bradenmacdonald I see you will be a core committer for this, thanks!

[bradenmacdonald]

@arbrandes Welcome back. Can you please rebase this? I'll review it next week.

[bradenmacdonald]

@arbrandes ^ ping :) When you have some time.

[bradenmacdonald]

👍 Do you want me to merge now ?

• I tested this: ran make easyserver, tested, ran make testserver, ran tests. Did not test with multiple devstacks, just regular
• I read through the code
• I checked for accessibility issues: n/a
• Includes documentation: yep

[arbrandes]

@bradenmacdonald, this is good to merge, yes, thanks!

[openedx-webhooks]

@arbrandes 🎉 Your pull request was merged!

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