SI-6987 Fixes fsc compile server verbose output

Internally the fsc server code was setting a "verbose" flag, but it was
always false. Fixing that gives server's verbose output, but because the
output was buffered and not flushed the server's output wasn't seen
until the compile run was complete. This commit fixes the verbose flag
and flushes the server side output.
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.
Merge pull request #1951 from JamesIry/SI-6987_2.10.x

SI-6987 Fixes fsc compile server verbose output