docstring: function: lxc: Add 'Since version' metadata
docstring: function: lxc: Add 'Since version' metadata

Either create or append to existing docstring, the version (git tag)
that a given function was introduced in the format:

    Since: v1.2.3

Signed-off-by: Victor Toso <39b7599ff73bbf5db531748ba5250f21fa7120ff@redhat.com>
Reviewed-by: Peter Krempa <2cf5c04c61aa466e4a47bfedc747d17279c72ffc@redhat.com>

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