Added --shard-target-runtime option to ew-cli. It’s a new sharding mode where you specify
the overall runtime instead of the number of shards. E.g. a 10-min test suite will spawn 5 shards
and finish around 2 minutes when invoked with --shard-target-runtime 2m
When running with --num-flaky-test-attempts we no longer re-run whole shards but only the tests
that failed. You can revert to the whole behaviour by adding --flaky-test-repeat-mode all.
