qemu_kill_report: Report PID name too

When qemu is being killed, its last words are:

2016-08-31T11:48:15.293587Z qemu-system-x86_64: terminating on signal 15 from pid 11180

That's nice, but what process is 11180? What if I told you we can
do better:

2016-08-31T11:48:15.293587Z qemu-system-x86_64: terminating on signal 15 from pid 11180 (/usr/sbin/libvirtd)

And that's exactly what this patch does.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Message-Id: <a2ba85a8e349a0ea9ee06424226197a03cd04bd3.1474987617.git.mprivozn@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

vl.c

@@ -1675,8 +1675,12 @@ static void qemu_kill_report(void)
              */
             error_report("terminating on signal %d", shutdown_signal);
         } else {
-            error_report("terminating on signal %d from pid " FMT_pid,
-                         shutdown_signal, shutdown_pid);
+            char *shutdown_cmd = qemu_get_pid_name(shutdown_pid);
+
+            error_report("terminating on signal %d from pid " FMT_pid " (%s)",
+                         shutdown_signal, shutdown_pid,
+                         shutdown_cmd ? shutdown_cmd : "<unknown process>");
+            g_free(shutdown_cmd);
         }
         shutdown_signal = -1;
     }