Dashes for zero latency values in zpool iostat -p

This prints dashes instead of zeros for zero latency values in
'zpool iostat -p'.  You'll get zero latencies reported when the
disk is idle, but technically a zero latency is invalid, since you
can't measure the latency of doing nothing.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Closes #6210

cmd/zpool/zpool_main.c

@@ -3460,7 +3460,7 @@ print_iostat_latency(iostat_cbdata_t *cb, nvlist_t *oldnv,
 	nva = calc_and_alloc_stats_ex(names, ARRAY_SIZE(names), oldnv, newnv);
 
 	if (cb->cb_literal)
-		format = ZFS_NICENUM_RAW;
+		format = ZFS_NICENUM_RAWTIME;
 	else
 		format = ZFS_NICENUM_TIME;