During setup of sharded cluster python fixture, we spawn several mongod/mongos processes, and we do this serially. When the test cluster contains many shards and several replicaset nodes, this can take very long time.

To speed the fixture setup phase, we can spawn the different processes in the cluster in parallel. This will contribute to reduce the time to wait for the fixture setup to complete and thus reduce considerably the time it takes to run a JS test.

These are the numbers that characterize the setup of a cluster made of  1 mongos, 1 config server and 2 shards with 3 nodes each:

• [Current] Serial setup: ~25 secs
• [Optimized] Parallel setup: ~9.5 secs