Migrate tests owned by CAR from SConstruct to Bazel.

This ticket includes sharding test fixtures (sharding_mongod_test_fixture, shard_server_test_fixture, config_server_test_fixture, sharding_test_fixture_common, sharding_mongos_test_fixture) as well as tests trivially unlocked by it. It does not include db_s_config_server_test and s_test as those have unconverted dependencies by other teams. The motivation for converting the sharding text fixtures as soon as possible is that they unblock migrations by other teams.

Benchmarks (env.Benchmark(...) / *_bm targets) will also be handled separately as there is no support for building them with Bazel yet.