Sessions are expected to only have one running query (perhaps this is a
bug). So we need to make a new session for each of the benchmark runs,
timing only the running part.
Given that there may be other Turing complete query interfaces
(particularly a Go query API), the timeout config should not be
specifically tied to gremlin.
Having a time.Duration measuring seconds is likely to cause problems at
a later stage. This change retains configuration compatibility while
adding idiomatic duration use.
