Enable time based benchmarks on redis-benchmark-go

[filipecosta90]

We should support time-based benchmarks ( and not only operation count based benchmarks ).
We should have the same look and feel as memtier_benchmark, meaning it's mandatory that the flag is --test-time.

--test-time=SECS           Number of seconds to run the test

[ninuxer]

I did this by running this command

timeout -s SIGINT ${YOUR SECS} redis-benchmark-go -l