docs: migration: Fix example for unix socket migration
docs: migration: Fix example for unix socket migration

Fix the following issues:

1) the very long line is overflowing the code box
2) '--migrateuri' was missing for the qemu data stream
3) '--desturi' was not used making it non-obvious what the argument
   corresponds to

Signed-off-by: Peter Krempa <2cf5c04c61aa466e4a47bfedc747d17279c72ffc@redhat.com>
Reviewed-by: Ján Tomko <4cab11cfb98d3c937327354a78eb07dbb6ee2bc6@redhat.com>

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