qemu-option: qemu_opts_create(): use error_set()

This commit converts qemu_opts_create() from qerror_report() to
error_set().

Currently, most calls to qemu_opts_create() can't fail, so most
callers don't need any changes.

The two cases where code checks for qemu_opts_create() erros are:

 1. Initialization code in vl.c. All of them print their own
    error messages directly to stderr, no need to pass the Error
    object

 2. The functions opts_parse(), qemu_opts_from_qdict() and
    qemu_chr_parse_compat() make use of the error information and
    they can be called from HMP or QMP. In this case, to allow for
    incremental conversion, we propagate the error up using
    qerror_report_err(), which keeps the QError semantics

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Reviewed-By: Laszlo Ersek <lersek@redhat.com>
diff --git a/qemu-config.c b/qemu-config.c
index be84a03..f876646 100644
--- a/qemu-config.c
+++ b/qemu-config.c
@@ -709,7 +709,7 @@
         return -1;
     }
 
-    opts = qemu_opts_create(&qemu_global_opts, NULL, 0);
+    opts = qemu_opts_create(&qemu_global_opts, NULL, 0, NULL);
     qemu_opt_set(opts, "driver", driver);
     qemu_opt_set(opts, "property", property);
     qemu_opt_set(opts, "value", str+offset+1);
@@ -781,7 +781,7 @@
             list = find_list(lists, group);
             if (list == NULL)
                 goto out;
-            opts = qemu_opts_create(list, id, 1);
+            opts = qemu_opts_create(list, id, 1, NULL);
             continue;
         }
         if (sscanf(line, "[%63[^]]]", group) == 1) {
@@ -789,7 +789,7 @@
             list = find_list(lists, group);
             if (list == NULL)
                 goto out;
-            opts = qemu_opts_create(list, NULL, 0);
+            opts = qemu_opts_create(list, NULL, 0, NULL);
             continue;
         }
         if (sscanf(line, " %63s = \"%1023[^\"]\"", arg, value) == 2) {