This adds a new flag, VIR_MIGRATE_PAUSED, that mandates pausing
the migrated VM before starting it.

* include/libvirt/libvirt.h.in (virDomainMigrateFlags): Add VIR_MIGRATE_PAUSED.
* src/qemu/qemu_driver.c (qemudDomainMigrateFinish2): Handle VIR_MIGRATE_PAUSED.
* tools/virsh.c (opts_migrate): Add --suspend. (cmdMigrate): Handle it.
* tools/virsh.pod (migrate): Document it.