Add benchmarks for generation and fingerprinting

Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)
Don't record generation time on fingerprint bench

Docker-DCO-1.1-Signed-off-by: Josh Hawn <josh.hawn@docker.com> <github: jlhawn)
Merge pull request #41 from dmcgowan/key_benchmarks

Add benchmarks for generation and fingerprinting