Skip -bgl versions in version_import script

[GregKaleka]

Fixes #1453

• Added "-bgl" to list of exclusion strings
• Added test case to existing test
• Made CELERY_TASK_ALWAYS_EAGER configurable via env var for debugging purposes

Manual testing

Ran import_versions command after fix to verify the version was not imported.

Post-deploy task

We'll need to manually delete this version on staging and prod for it to actually disappear from the dropdown.