Removed the remaining uses of older TestClient construction methods in favor of Client::test_builder
Cleaned up the additional_options tangle: moved the LB-specific initialization to be internal to the v2 test runner (the only thing that actually needed it / was using it) and provided the much simpler sharded_use_first_host for all the other places it was being called.
With this done, there's now only one way to make a TestClient and only one way to set options for it :)
RUST-1449
Two main themes of changes in this PR:
TestClientconstruction methods in favor ofClient::test_builderadditional_optionstangle: moved the LB-specific initialization to be internal to the v2 test runner (the only thing that actually needed it / was using it) and provided the much simplersharded_use_first_hostfor all the other places it was being called.With this done, there's now only one way to make a
TestClientand only one way to set options for it :)