Failed worker protocol error doesn't explain that stdout is reserved for worker protocol

[alexeagle]

When a user just adds a console.log to a nodejs worker (or System.out.println to a Java one) they get a big error that looks to them like they crashed Bazel, and no indication that a Worker process is not allowed to write things to stdout.

This makes it very hard to recover from a basic attempt to debug problems.

(It helps a lot that we now print the thing that was written to stdout, like no ivy below, but it's hard to find unless you're accustomed to parsing this error, and still doesn't say how to fix it)

ERROR: /home/www/angular/packages/core/BUILD.bazel:5:1: Compiling Angular templates (ngc) //packages/core:core failed: Worker process returned an unparseable WorkResponse:

---8<---8<--- Exception details ---8<---8<---
com.google.protobuf.InvalidProtocolBufferException$InvalidWireTypeException: Protocol message tag had invalid wire type.
	at com.google.protobuf.InvalidProtocolBufferException.invalidWireType(InvalidProtocolBufferException.java:115)
	at 
 ...
com.google.devtools.build.skyframe.AbstractParallelEvaluator$Evaluate.run(AbstractParallelEvaluator.java:340)
	at com.google.devtools.build.lib.concurrent.AbstractQueueVisitor$WrappedRunnable.run(AbstractQueueVisitor.java:352)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)
---8<---8<--- End of exception details ---8<---8<---

---8<---8<--- Start of log ---8<---8<---
no ivy
---8<---8<--- End of log ---8<---8<---

[cushon]

A better diagnostic would be helpful, but the problem could also be avoided by not using stdout to communicate with workers, e.g. #2832

[philwo]

@cushon Absolutely. Unfortunately I won't have time to work on that before Q3. :|

I prepared a fix for this that adds a more helpful message in this case.