QemuOpts: Drop qemu_opt_set(), rename qemu_opt_set_err(), fix use

qemu_opt_set() is a wrapper around qemu_opt_set() that reports the
error with qerror_report_err().

Most of its users assume the function can't fail.  Make them use
qemu_opt_set_err() with &error_abort, so that should the assumption
ever break, it'll break noisily.

Just two users remain, in util/qemu-config.c.  Switch them to
qemu_opt_set_err() as well, then rename qemu_opt_set_err() to
qemu_opt_set().

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
diff --git a/util/qemu-config.c b/util/qemu-config.c
index b13efe2..f3463df 100644
--- a/util/qemu-config.c
+++ b/util/qemu-config.c
@@ -219,6 +219,7 @@
 
 int qemu_set_option(const char *str)
 {
+    Error *local_err = NULL;
     char group[64], id[64], arg[64];
     QemuOptsList *list;
     QemuOpts *opts;
@@ -242,7 +243,9 @@
         return -1;
     }
 
-    if (qemu_opt_set(opts, arg, str+offset+1) == -1) {
+    qemu_opt_set(opts, arg, str + offset + 1, &local_err);
+    if (local_err) {
+        error_report_err(local_err);
         return -1;
     }
     return 0;
@@ -335,7 +338,9 @@
                 error_report("no group defined");
                 goto out;
             }
-            if (qemu_opt_set(opts, arg, value) != 0) {
+            qemu_opt_set(opts, arg, value, &local_err);
+            if (local_err) {
+                error_report_err(local_err);
                 goto out;
             }
             continue;