Due to the current integration of mongot setup in python test fixture, we are forced to spawn routers (mognos binary) after the shards (mongod binary).

As also explained in this comment this is because the mongot parameters (namely mongot port) is decided during the setup of the shard replicaset fixture.

The goal of this ticket is to re-organize the mongot startup code so that the mongot parameters are already known when ShardedClusterFixture::setup() function is called. This allows us to spawn both mongos and mongod binaries concurrently.