Use assignment creator's token when random token fails

[EricPickup]

What

Back-end solution to #2222

When creating a repo for a student, grab a random classroom admin's token (as we currently do).

If the token can access the repo, use that token to create the student repo. Otherwise use the assignment creator's token.

[EricPickup]

Update since today is my last day 😢

I held off on this PR since I found some weird behavior testing it locally.

To reproduce:

1. Create a classroom with two administrators
2. Create an assignment within that classroom using a private starter code repo that only Admin 1 can access
3. Try to accept that assignment. It will recognize that not all admins have access and will use the assignment creator (admin 1's) octokit client, but I'm still getting a 403 forbidden even with the proper client.

This might be some weird issues on my environment.

Once this is fixed I suggest adding this under a feature flag to be safe.

[spinecone]

I've been getting my local environment to test the weird behavior Eric mentioned. So far I haven't reproduced it (the assignment was successfully accepted) but will keep trying tomorrow.

[spinecone]

I dug around in the console and it looks like the Resource could not be found on github.com error is coming from when we try to look at the organization plan, since the GithubOrganization we create around the assignment creator's token isn't a real organization.

[spinecone]

Rather than creating a fake GithubOrganization around the assignment creator's token and needing to worry about other places where we expect it to behave like an organization (such as checking if it has a free/paid plan, which the fake org returns nil for), I'm working on thinking of a different approach for this problem.

Instead of changing which GithubOrganization object calls create_repository, it might make more sense for us to continue just using the real organization that owns the assignment, and having it try the assignment creator's token itself if it doesn't have access with its own random token.

def create_repository(repo_name, alternate_client, users_repo_options = {})
  repo_options = github_repo_default_options.merge(users_repo_options)

  repo = GitHub::Errors.with_error_handling do
    begin
      @client.create_repository(repo_name, repo_options)
    rescue GitHub::Error
      use_alternate_client = true
      # Try the assignment creator's token before giving up
      alternate_client.create_repository(repo_name, repo_options)
    end
  end

  GitHubRepository.new(use_alternate_client ? alternate_client : @client, repo.id)
end