OpenID auth broken in jwtUtil

Moving from v0.6.3 to master, it looks like the OpenID auth was refactored into jwtUtil. However, this no longer works with providers that do not use `unique_name` by default such as Google. In v0.6.3, any valid claim was used as the username, while in v0.7.0 only the claim `unique_name` is allowed to be the username. See,

https://github.com/HDFGroup/hsds/blob/9e1f08183f6f5e7ad51c57a6d2e7ba0ecfd95f02/hsds/util/jwtUtil.py#L177-L191

The v0.6.3 behavior wasn't great so I understand why it was changed, but this needs to be configurable. Possible options:
- The first listed claim is used as the username field (possibly only if `unique_name` isn't present)
- Add a new config option `openid_username_claim` and maybe also `openid_roles_claim`