bitbake: server/process: Various server startup logging fixes

There were various problems in the server startup loggin:

a) stdout/stderr were not being flushed before forking which could potentially
   duplicate output

b) there were separate buffers for stdout/stderr leading to confusing logs
   where the entries could be reordered. This was particularly confusing
   due to the separator the logs use to idendify new messages

c) an fd wasn't being closed during server startup meaning if the
   server failed to start, the closed fd wasn't detected as it was held
   open by the other reference

d) If the pipe was detected as being closed, the code incorrectly retried
   server startup

e) The event code would remap stdout/stderr without flushing them, leading
   to lose log messages

(Bitbake rev: 0594faa0b52ce5dbd948d836d88617d38d9862d1)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/event.py

@@ -141,6 +141,9 @@ def print_ui_queue():
     logger = logging.getLogger("BitBake")
     if not _uiready:
         from bb.msg import BBLogFormatter
+        # Flush any existing buffered content
+        sys.stdout.flush()
+        sys.stderr.flush()
         stdout = logging.StreamHandler(sys.stdout)
         stderr = logging.StreamHandler(sys.stderr)
         formatter = BBLogFormatter("%(levelname)s: %(message)s")