migrate: move max-bandwidth and downtime-limit to migrate_set_parameter

Mark the old commands 'migrate_set_speed' and 'migrate_set_downtime' as
deprecated.
Move max-bandwidth and downtime-limit into migrate-set-parameters for
setting maximum migration speed and expected downtime limit parameters
respectively.
Change downtime units to milliseconds (only for new-command) and set
its upper bound limit to 2000 seconds.
Update the query part in both hmp and qmp qemu control interfaces.

Signed-off-by: Ashijeet Acharya <ashijeetacharya@gmail.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
