qemu: Implement VIR_MIGRATE_POSTCOPY_RESUME for Begin phase
qemu: Implement VIR_MIGRATE_POSTCOPY_RESUME for Begin phase

Mostly we just need to check whether the domain is in a failed post-copy
migration that can be resumed.

Signed-off-by: Jiri Denemark <62bdf77dc47919a4d59a91822129d14633cfca81@redhat.com>
Reviewed-by: Peter Krempa <2cf5c04c61aa466e4a47bfedc747d17279c72ffc@redhat.com>

jfehlig/libvirt,olafhering/libvirt,libvirt/libvirt,crobinso/libvirt,zippy2/libvirt,crobinso/libvirt,jfehlig/libvirt,olafhering/libvirt,zippy2/libvirt,libvirt/libvirt,olafhering/libvirt,jfehlig/libvirt,libvirt/libvirt,jfehlig/libvirt,olafhering/libvirt,libvirt/libvirt,crobinso/libvirt,zippy2/libvirt,crobinso/libvirt,zippy2/libvirt