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.

No reviewer requested until the build kitteh can verify the test works reliably.