As a Bazel user I want a test suite Bazel rule to package multiple test target and run them in parallel

[chenxiao0228]

Today we have bptestrunner to split a test target and run it in multiple simulators in parallel.

But when we have multiple test target the cost to spawn simulators and install app hosts is high. We would like to have a Bazel rule that's basically an equivalent of an xcscheme that bundles multiple test bundles into multiple test hosts. Combining that with the clone simulator feature we can save a lot of time spawning simulators.