https://jira.mongodb.org/browse/SERVER-112726 enabled random balancing in sharded_collections_jscore_passthrough_with_config_transitions_and_add_remove_shard.yml and sharding_jscore_passthrough_with_config_transitions_and_add_remove_shard.yml.

Following properties were enabled in ShardedClusterFixture
enable_balancer: true
random_migrations: true

After this change, several tests began failing because the balancer and random migrations can trigger unexpected errors that the tests were not designed to handle.