Avoid session reuse when new token is needed

[bbockelm]

Motivation

In testing of rucio upload, I've sporadically hit cases where:

1. In a sequence of REST API calls, one call requires the client to retrieve a new Rucio token.
2. The client will contact the token issuer endpoint to retrieve a new token.
3. Since the client reuses the session object, an existing SSL session may be utilized.
4. If the existing SSL session wasn't created with an X509 user proxy (or established via TLS session reuse), then mod_gridsite isn't able to pass along the appropriate headers about the client DN.
5. Without the client DN, the issuer (correctly) refuses to issue a new token.

Modification

Whenever the client receives an authorization failure, it should create a new session object prior to retrying the token retrieval.