Purge migration of (almost) everything to do with monitors

The Monitor object is passed back and forth within the migration/savevm
code so that it can print errors and progress to the user.

However, that approach assumes a HMP monitor, being completely invalid
in QMP.

This commit drops almost every single usage of the Monitor object, all
monitor_printf() calls have been converted into DPRINTF() ones.

There are a few remaining Monitor objects, those are going to be dropped
by the next commit.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
