r/vmhost: Update for latest libvirt

Some time ago, _libvirt_ was refactored to use separate daemons and
sockets for each of its responsibilities, and the original "monolithic"
`libvirtd` was made obsolete.  The Fedora packages have more recently
been adjusted to favor this new approach, and now default to omitting
the monolithic daemon entirely (when `install_weak_deps` is disabled).

One interesting packaging snafu, though, is that without the weak
dependencies, there is _no_ way for clients to connect by default.
Clients run `which virt-ssh-helper` to see if it is installed, which it
is, but `which` is not.  They then fall back to running `nc`, which is
_also_ not installed.  So even though the tools they actually need are
present, their logic for detecting this is broken.  As such, we need to
explicitly install `which` to satisfy them.

roles/vmhost/vars/main.yml

@@ -5,6 +5,8 @@ vmhost_required_packages:
 - python3-libvirt
 - python3-lxml
 - qemu-audio-spice
+- qemu-char-spice
 - qemu-device-display-qxl
 - qemu-device-display-virtio-vga
 - qemu-system-x86-core
+- which