SI-6987 Tests fsc verbose output

This commit includes a test of fsc's verbose output. In order for it
to work, CompileServer's main method had to be modified to remove a
sys exit 0 at the end. It was redundant and made testing a bit harder.

In order to prevent a race condition between server and client start
up, this commit also adds a server callback that decrements a
CountDownLatch that the main testing thread waits for.

Finally, the server had to be modified to use Console.withErr
and Console.withOut instead of mutating the global System.err
and System.out variables. Otherwise the test would be unreliable.

1 files changed, 1 insertions, 0 deletions

diff --git a/test/files/run/t6987.check b/test/files/run/t6987.check
new file mode 100644
index 0000000000..86fc96c679
--- /dev/null
+++ b/test/files/run/t6987.check
@@ -0,0 +1 @@
+got successful verbose results!