Add --output-format command line option

Right now we have normal, terse, and json output. Lets add a parameter
that controls how to output results, instead of having options for
both terse and json outputs. If we are going to add a 4th output
type in the future, it's only going to get more messy.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/eta.c b/eta.c
index 1caee49..075ce8c 100644
--- a/eta.c
+++ b/eta.c
@@ -264,7 +264,9 @@
 	static struct timeval rate_prev_time, disp_prev_time;
 
 	if (!force) {
-		if (temp_stall_ts || terse_output || eta_print == FIO_ETA_NEVER)
+		if (output_format != FIO_OUTPUT_NORMAL)
+			return 0;
+		if (temp_stall_ts || eta_print == FIO_ETA_NEVER)
 			return 0;
 
 		if (!isatty(STDOUT_FILENO) && (eta_print != FIO_ETA_ALWAYS))