`--strategy=SingleJar=worker` errors

[andyscott]

In a new project, using --strategy=SingleJar=worker results in build failures:

Worker process did not return a WorkResponse

It seems there's some flag incompatibilities that'll need to be documented.

[pauldraper]

Odd. It appears that it intends to support workers. https://github.com/bazelbuild/bazel/blob/master/src/java_tools/singlejar/java/com/google/devtools/build/singlejar/SingleJar.java