Tezt/Cloud/DAL: Fix metric of bakers when stake ratio is small
What
Fix the metrics related to attestation ratio from bakers when their stake is rather low.
Why
When the stake of the baker is low, there is a non-negligible chance the baker does not get any assigned shards. The current metrics did not compute this case correctly.
How
We change the metrics computation so that when a baker does not get assigned any shards, this does not affect the ratio.
Manually testing the MR
Run the test with a baker having 1% of the stake.