Do performance benchmark testing as part of build

[ericwb]

Is your feature request related to a problem? Please describe.
Bandit could use some more focus on being performant. Currently there really isn't any testing of performance other than user feedback.

Describe the solution you'd like
I'd like to see a job in tox and the CI to run benchmark tests. This can establish a baseline such that we can focus on improving the results.

Describe alternatives you've considered
n/a

Additional context
It's unclear which tool would be best to run benchmarking on Bandit. There is pytest-benchmark but believe it makes use of pytest. Bandit currently uses stestr.

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