tests: re-run only failed test cases in A/B test

Instead of re-running the whole suite, with this commit we're only
re-running the specific tests that regressed.
This will speed up the runtime of A/B tests.

In order to do so, this commit adds a new `nodeid` field to `metrics
.json`, so we can correctly identify which test case produced which
metric.

Signed-off-by: Marco Marangoni <mamarang@amazon.com>