migration: Add state records for migration incoming

migration: Add state records for migration incoming

For migration destination, we also need to know its state,
we will use it in COLO.

Here we add a new member 'state' for MigrationIncomingState,
and also use migrate_set_state() to modify its value.

Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
dgilbert: Fixed early free of MigraitonIncomingState
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
Message-Id: <1450266458-3178-3-git-send-email-dgilbert@redhat.com>
Signed-off-by: Amit Shah <amit.shah@redhat.com>