Add option to turn on JSON pretty printing in monitor

Expaned '-mon' arg to allow a 'pretty=on' flag. This makes the
monitor pretty print its replies to easy human debugging / reading

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
diff --git a/vl.c b/vl.c
index d352d18..939ee87 100644
--- a/vl.c
+++ b/vl.c
@@ -1562,6 +1562,9 @@
         exit(1);
     }
 
+    if (qemu_opt_get_bool(opts, "pretty", 0))
+        flags |= MONITOR_USE_PRETTY;
+
     if (qemu_opt_get_bool(opts, "default", 0))
         flags |= MONITOR_IS_DEFAULT;