Revert "monitor: Convert do_migrate_set_speed() to QObject"

Revert "monitor: Convert do_migrate_set_speed() to QObject"

This reverts commit 3a4921047d514c336531c304bec362c4d138ebcc.

From Luiz:

  do_migrate_set_speed() accepts a suffix for the 'value' argument and this is
  not good for QMP.  We will have to add a new argument type to handle that and
  this will have to wait for 0.13.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
(cherry picked from commit 46ee2295678af629a2869e4e331e4e002bcc31fd)