Catch OAuthError for API calls with bad authorisation details

[Michael Nelson]

Currently in reviewsapp.auth.SSOOAuthAuthentication.validate_token we don't catch any possible exceptions when calling:

oauth_server.verify_request

We should catch any OAuthErrors and return a 401

STR:
1) setup the SC client to use the wrong USSOC_SERVICE_URL (in run_against_rnr_testing_env.sh) for the environment you are testing,
2) try to submit a review
3) check the console from which SC was run for the error status code

ER: 401
AR: 500