Investigate and fix redhat import failure

[sbs2001]

The redhat importer is still failing after the fix at #387.

From the logs at https://pipelines.actions.githubusercontent.com/Ep9prel8NYELDl3abhBbfgiORCbX0JuViN8i8esKzVS8DdQt5i/_apis/pipelines/1/runs/151/signedlogcontent/3?urlExpires=2021-03-24T04%3A20%3A33.2100559Z&urlSigningMethod=HMACV1&urlSignature=7VXaMaJelaCEUG6EDzDbZKLAw%2BfWbGUypuHe164RCjE%3D

It seems there is problem at https://github.com/nexB/vulnerablecode/blob/bfa005ece230ada9032c3c0b4a7bab7b59673e0b/vulnerabilities/importers/redhat.py#L93.

To fix this:

1.Find the cause of 443
2.Add a workaround on non-json response .

[Hritik14]

I'm working on it

[Hritik14]

Update: I ran the importer for 6 hours straight and it wasn't responding after the fetching.
Either the amount of advisories is so high that it's taking lot of time to actually import (#210) or it's something else.

I'll investigate further by Monday.

[Hritik14]

Update: The root cause is abusing the server with so many requests in such a short time. The server is replying with 502: Proxy Error and sometimes with 104: Connection reset. I'm implementing a requests helper to retry with sane back-offs on such situations.
I've also mailed bugzilla-owner@redhat.com to ask if there exists any scraping restrictions in a given time.

[Hritik14]

Update: Today I woke up to this and I'm happy :D