in XAPI's installation, nova tarball does not contain any xen plugin since newton.

in this section:
https://docs.openstack.org/newton/config-reference/compute/hypervisor-xen-api.html#install-xapi-plug-ins

$ NOVA_URL=https://tarballs.openstack.org/nova/nova-master.tar.gz
$ wget -qO "$NOVA_TARBALL" "$NOVA_URL"
$ tar xvf "$NOVA_TARBALL" -d "$NOVA_SOURCES"

NOVA_URL is the newest version of nova-master tarball. There is not any xapi plugin in it since newton.

This bug tracker is for errors with the documentation, use the following as a template and remove or add fields as you see fit. Convert [ ] into [x] to check boxes:

- [x] This doc is inaccurate in this way: ______
- [ ] This is a doc addition request.
- [ ] I have a fix to the document that I can paste below including example: input and output.

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-----------------------------------
Release: 0.9 on 2018-01-26 00:18
SHA: 3d7f0be2be0108912bae26e9333e825d929f4943
Source: http://git.openstack.org/cgit/openstack/openstack-manuals/tree/doc/config-reference/source/compute/hypervisor-xen-api.rst
URL: https://docs.openstack.org/newton/config-reference/compute/hypervisor-xen-api.html