trace: split trace_init_file out of trace_init_backends

This is cleaner, and improves error reporting with -daemonize.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Denis V. Lunev <den@openvz.org>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Message-id: 1452174932-28657-4-git-send-email-den@openvz.org
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/qemu-io.c b/qemu-io.c
index 1c11d57..83c48f4 100644
--- a/qemu-io.c
+++ b/qemu-io.c
@@ -435,7 +435,7 @@
             }
             break;
         case 'T':
-            if (!trace_init_backends(optarg)) {
+            if (!trace_init_backends()) {
                 exit(1); /* error message will have been printed */
             }
             break;