* Mark S2A public APIs as experimental.
* Rename S2AChannelCredentials createBuilder API to newBuilder.
* Remove usage of AdvancedTls.
* Use InsecureChannelCredentials.create instead of Optional.
* Invoke Thread.currentThread().interrupt() in a InterruptedException block.
* S2AHandshakerServiceChannel doesn't use custom event loop.
* use executorPool.
* log when channel not shutdown.
* use a cached threadpool.
* update non-executor version.
Move unused and unimportant fields to local variables. pickUnusedPort()
is inherently racy, so avoid using it when unnecessary. The channel's
default executor is fine to use, but if you don't like it
directExecutor() would be an option too. But blocking stub doesn't even
use the executor for unary RPCs. Thread.join() does not propagate
exceptions from the Thread; it just waits for the thread to exit.
Riya Mehta
Eric Anderson
Larry Safran