Update django-oauth-toolkit rockstor#2710

Remove pinning for django-oauth-toolkit and remove
explicit declaration of oauthlib as it is a
dependency of django-oauth-toolkit.

Re-address prior work-around for older oauth2_provider
migration file silently failing to apply and holding up
all subsequent oauth2_provider migrations, as this migration
file, and a few subsequent ones, have now been squashed upstream.
"oauth2_provider" is part of django-oauth-toolkit.

Added dev logging for before/after our migration in this area.