Since bonafide was not catching the error 401, an attempt to bootstrap a
provider that does not support anonvpn with the new setup was resulting
in a json that was containing only an error message.

this was producing an error when trying to access the configuration for
that provider's EIP section.

we now avoid writing a json config file if an error 401 is found, and
also catch the exception for a ValueError when the EIP section is not
found in the provider's configuration.

honor the anonymous certificate for the providers that offer it.
this still needs a change in bonafide, in which if provider supports
anonymous access we still have to download eip-service.json

for testing, I assume this has been already manually downloaded.

This deferred was not used anywhere, but it was called twice.
Provider is a singleton so multiple logins into the same provider where
producing it to be called mor than once.

- Resolves: #9171

Pin the provider.json and the ca cert for the public providers.

- Resolves: #9074

There was common situations where two provider instances where running
in parallel. And was creating weird errors (like getting wrong api_uri)
because the bootstrap deferreds were global but the Provider objects
not.

I don't like much singletons, but I think now is simpler than before.

- Resolves: #9073

whoever wrote this in the first place needs to get introduced to
import-time initialization, even if it was me. one of the nastiest
python gotchas in my opinion :)

just to make the logic clear.
we should probably check that the file is not empty and it has valid
json (sanitized against the spec).

here we port the if-modified-since conditional mechanism, so that we
only write the config if it is newer than whan we have.

we also add a line with the status code to the logs, so that it's easier
to debug.

note that the 'configs.json' file is never returning 304.

- Resolves: #8773