Comment 12 for bug 457163

Upstream actually has completion, and we ship it since cosmic IIRC.

From the build:
checking for BASH_COMPLETION... yes
checking for bash-completions directory... /usr/share/bash-completion/completions

configure: bash_completion: yes (CFLAGS='' LIBS='')

/usr/bin/install -c ../../../tools/bash-completion/vsh \
 "/<<PKGBUILDDIR>>/debian/tmp/usr/share/bash-completion/completions/vsh"
( cd /<<PKGBUILDDIR>>/debian/tmp/usr/share/bash-completion/completions && \
 rm -f virsh virt-admin && \
 ln -s vsh virsh && \
 ln -s vsh virt-admin )

Since
libvirt (4.5.0-1) unstable; urgency=medium
  * [882c646] Install bash completion (Closes: #902450)

That said in Cosmic I have it all working as intented:
ubuntu@c:~$ virsh l
list lxc-enter-namespace
ubuntu@c:~$ virsh list --
--all --managed-save --persistent --state-running --title --with-managed-save --without-snapshot
--autostart --name --state-other --state-shutoff --transient --with-snapshot
--inactive --no-autostart --state-paused --table --uuid --without-managed-save
ubuntu@c:~$ virsh list --a
--all --autostart