tests/perf_fast_forward: add an option to dump all results
tests/perf_fast_forward: add an option to dump all results

perf_fast_forward runs each test case multiple times and reports a
summary of those results (median, min, max, and median absolute
deviation).

While very convenient the summary may hide some important information
(e.g. the distribution of the results). This patch adds an option to
report results of every single executed iteration.

scylladb/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla