Summary:
The snapshot is marked as done in the MasterSnapshotCoordinator as soon as it is created on all tablets, but is only added to tablet_to_covering_snapshots_ asynchronously after the sys catalog write updating the state is stored to RocksDB.
While tablet_to_covering_snapshots_ is updated after snapshots is stored to RocksDB.
So it could happen that test see snapshot as completed, but tablet_to_covering_snapshots_ is empty.

Fixed by updating tablet_to_covering_snapshots_ while snapshot is marked as done.
Jira: DB-14446

Test Plan: ./yb_build.sh release -n 400 --cxx-test integration-tests_snapshot-test --gtest_filter SnapshotTest.HideTablesCoveredBySnapshot -- -p 16

Reviewers: hsunder, mhaddad, asrivastava

Reviewed By: asrivastava

Subscribers: ybase

Tags: #jenkins-ready

Differential Revision: https://phorge.dev.yugabyte.com/D40928