Benchmark to validate a keystone token N times at service endpoint

With PKI, tokens can be validated at the service endpoint. There might
be some caching policies which might affect the validation process.
This benchmark can be used to check effect of caching related to tokens.

Change-Id: I6277d8514bbdb1e5dca5032f44ac3d5ff9618cc2
Merge "Benchmark to validate a keystone token N times at service endpoint"