If ignore-shared capability is set then skip shared RAMBlocks during the
RAM migration.
Also, move qemu_ram_foreach_migratable_block (and rename) to the
migration code, because it requires access to the migration capabilities.

Signed-off-by: Yury Kotov <yury-kotov@yandex-team.ru>
Message-Id: <20190215174548.2630-4-yury-kotov@yandex-team.ru>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>