Fix CPU hotplug command names

Probably as a result of a merge error, the CPU hotplug command
names were completely wrong.

* src/qemu/qemu_monitor_json.c, src/qemu/qemu_monitor_text.c: Fix
  the CPU hotplug command names

src/qemu/qemu_monitor_json.c

@@ -1181,7 +1181,7 @@ int qemuMonitorJSONSetCPU(qemuMonitorPtr mon,
                           int cpu, int online)
 {
     int ret;
-    virJSONValuePtr cmd = qemuMonitorJSONMakeCommand("balloon",
+    virJSONValuePtr cmd = qemuMonitorJSONMakeCommand("cpu_set",
                                                      "U:cpu", (unsigned long long)cpu,
                                                      "s:state", online ? "online" : "offline",
                                                      NULL);

src/qemu/qemu_monitor_text.c

@@ -800,7 +800,7 @@ int qemuMonitorTextSetBalloon(qemuMonitorPtr mon,
 
 
 /*
- * Returns: 0 if balloon not supported, +1 if balloon adjust worked
+ * Returns: 0 if CPU hotplug not supported, +1 if CPU hotplug worked
  * or -1 on failure
  */
 int qemuMonitorTextSetCPU(qemuMonitorPtr mon, int cpu, int online)
@@ -809,7 +809,7 @@ int qemuMonitorTextSetCPU(qemuMonitorPtr mon, int cpu, int online)
     char *reply = NULL;
     int ret = -1;
 
-    if (virAsprintf(&cmd, "set_cpu %d %s", cpu, online ? "online" : "offline") < 0) {
+    if (virAsprintf(&cmd, "cpu_set %d %s", cpu, online ? "online" : "offline") < 0) {
         virReportOOMError();
         return -1;
     }