mbox_log_console(): Add explicit fflush() for stdout

stdout is line-buffered by default while stderr is not. Additionally the
logging infra was switching between stderr and stdout based on the
severity of the message. Make sure we flush stdout if necessary.

Change-Id: I9649e1aa20dca6220cdd5ca91f2bab2a99b24aac
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
diff --git a/common.c b/common.c
index c0497fd..a5f6700 100644
--- a/common.c
+++ b/common.c
@@ -26,6 +26,9 @@
 	fprintf(s, "[%s %ld.%.9ld] ", PREFIX, time.tv_sec, time.tv_nsec);
 
 	vfprintf(s, fmt, args);
+
+	if (s == stdout)
+		fflush(s);
 }
 
 __attribute__((format(printf, 2, 3)))